feat(stalwart): MTA-STS routes as a maintainable list, in both routing modes

The policy route for mta-sts.<domain> belonged to another repository
(jk-cluster-config) while pointing at this chart's own Service. It moves
here as mtaSts.hosts, a list, so several domains - subdomains included -
are maintainable in one place and in whichever routing mode is active.

THE LIST IS THE SWITCH. No mtaSts.enabled: "enabled with an empty list"
would be a state with no meaning that the chart would then have to catch.
The schema rejects the key outright, so the rule is enforced rather than
documented. Default [] renders nothing in either mode - the defaults and
the unchanged CI fixture both produce a byte-identical helm template
against origin/main.

Entry form {host, tlsSecretName, clusterIssuer?}. The two TLS fields are
read ONLY in Ingress mode; in Gateway mode TLS sits on the listener, so
requiring them there would demand a value that does nothing.

THE PATH IS HARDWIRED. RFC 8461 fixes /.well-known/mta-sts.txt, rendered
with pathType Exact (type: Exact in the route). A values key for a
protocol-mandated path can only ever be set wrong, and wrong is invisible
from this side. Exact also matters in itself: a prefix on these hostnames
would publish the mail server's whole management surface under them.

ONE INGRESS PER CLUSTER ISSUER, NOT ONE OBJECT - and the plan's own three
requirements forced that. cert-manager reads the two fields at different
scopes: cluster-issuer is an ANNOTATION (object-scoped, and absent means
nothing is issued for that object at all), while secretName is
tls-entry-scoped and yields one Certificate per entry. So an object cannot
both request a certificate and leave another host's secret alone, which is
what an empty per-entry issuer has to mean. Measured in jk-cluster:
ingress-shim names the Certificate AFTER THE SECRET and owns it from the
Ingress, so a shared secret must sit in exactly one object (hence grouping
the tls list by secret, reusing rss-bridge.tlsGroups' shape) and a secret
may not span two issuer groups (hence the abort). Objects are named by
issuer, not by index: an index is only free where the object holds no
certificate, which is the precondition homeassistant's route naming states
for itself.

Gateway mode renders ONE HTTPRoute with every hostname - nothing differs
per host there - attached to the same Gateway(s) as the WebUI route.

WHAT THE CHART CANNOT PROMISE, AND THEREFORE NAMES: it registers a route,
it does not create a domain. The domains live in Stalwart's data store, so
an entry whose domain is missing there answers 404 at a correctly routed
endpoint with every object green - and MTA-STS failures are silent on the
SENDER's side, which delivers in the clear and logs nothing here. Same for
the _mta-sts.<domain> TXT record and the policy's content. The subdomain
trap is documented too: mta-sts.sub.<domain> is one label below
*.<domain>, so a parent wildcard certificate does not cover it.

Not folded into certificate.extraDnsNames deliberately - that would hang
the MAIL certificate on this list, letting a bad policy entry take STARTTLS
and IMAPS with it.

Minor, additive, empty default: 1.2.0+upv0.16.25 -> 1.3.0+upv0.16.25.

CI: ci/httproute/stalwart.yaml enters all three shapes of the entry form
(with issuer, without, and a subdomain), taking the HTTPRoute render test
from 56 assertions over 21 charts to 58 over 21 - stalwart from 2 to 4.
The Ingress half cannot be covered there, since an overlay's whole job is
to switch the mode off, so ci/stalwart/test-values.yaml carries two
entries and the install-test has a real API server accept them.

Fixes #123

README.md

@@ -181,7 +181,7 @@ Three things to know before touching it:
 - **What is deliberately not checked**, named so the gaps are not mistaken for coverage. *That traffic flows* — no Gateway controller runs in CI and none will, so `Accepted: True` is not obtainable; that claim is simply not made anywhere in this pipeline. *That any redirect is ever served* — the pairing check proves the rendered **object** carries a `RequestRedirect` rule on the bare prefix and nothing more: whether an implementation honours the `statusCode` or declines it and fails the whole route is outside what a render can see. *Mutual exclusion with the Ingress* — each chart aborts its own render when `ingress.enabled` and `httpRoute.enabled` are both true, which is where it belongs: this test renders one configuration per chart, and a rule here would have to assume the switch is chart-global, which may not survive the multi-app charts of the sweep. *Cross-namespace and non-Service backends*, and a rule with no `backendRefs` at all (legal for a filter-only rule) — all three are **reported as "not checked", never counted as passing**. The redirect rule the pairing check demands is itself backend-less, so a chart that satisfies that check also earns one "not checked" line; both verdicts are correct at once.
 - **Two anti-vacuum guards**, because the convention ships `httpRoute.enabled: false` and this test would otherwise be green over nothing. `ci/httproute/<chart>.yaml` is a render-only overlay applied **last** whose one job is to put a chart into Gateway mode — and a chart that *has* one and still renders no route **fails**. On top of that the run fails if **no assertion at all** held anywhere. `cyberchef` is exercised through its ordinary install-test fixture (which installs in Gateway mode, see below), every other converted chart through its overlay. For a multi-app chart the overlay also has to enter every shape the template has: `ci/httproute/freesailarr.yaml` moves one app onto a host of its own so that the shared-host route *and* the per-app route are both rendered.
 
-Measured in CI (run 719, the pilot): **30 charts, 4 assertions held**, whole job 13 s including checkout and the Helm setup, no cluster. Group 1 took that to 20 assertions over 10 charts and group 2 to 36 over 15; the prefix/redirect pairing of Gitea #118 adds the first check since the pilot rather than a chart, which brought it to 37 over 15 — one assertion for `freesailarr`'s `/qbittorrent`, plus one more "not checked" line for the backend-less redirect rule it demands. **Group 3 takes it to `56` assertions over `21` charts**, which is the sweep finished except for the frozen `rss-bridge`. Group 3's 19 come from six charts and three of them contribute more than one route: `keycloak` 4 (public and admin routes), `matrix-synapse` 4 (homeserver and delegation routes), `homeassistant` 5 (two routes, three rules — its overlay is the only one in the repo that has to *supply* hostnames, since the chart has no `ingress.domain`), `bulwark` 2, `stalwart` 2, `ytdlp-web-player` 2. The fail path was exercised rather than assumed: a Service renamed in the route, a port the Service does not expose, a port left out entirely, an emptied `parentRefs` with the chart's own guard disabled, an overlay that renders no route, a run with zero assertions, and — for the pairing — both the redirect rule deleted outright and the redirect pointed at a path other than the one stripped; each produced a `FAIL` naming both sides and a non-zero exit.
+Measured in CI (run 719, the pilot): **30 charts, 4 assertions held**, whole job 13 s including checkout and the Helm setup, no cluster. Group 1 took that to 20 assertions over 10 charts and group 2 to 36 over 15; the prefix/redirect pairing of Gitea #118 adds the first check since the pilot rather than a chart, which brought it to 37 over 15 — one assertion for `freesailarr`'s `/qbittorrent`, plus one more "not checked" line for the backend-less redirect rule it demands. **Group 3 takes it to `56` assertions over `21` charts**, which is the sweep finished except for the frozen `rss-bridge`. Gitea #123 then takes it to **`58` over `21`**: `stalwart` grows a second route for its MTA-STS policy hosts, so the assertion count moves while the chart count does not — a converted chart gaining an object is the ordinary way this figure grows from here on, and the overlay has to enter the new shape for it to count (`ci/httproute/stalwart.yaml` carries an entry with a `clusterIssuer`, one without, and one on a subdomain). Group 3's 19 come from six charts and three of them contribute more than one route: `keycloak` 4 (public and admin routes), `matrix-synapse` 4 (homeserver and delegation routes), `homeassistant` 5 (two routes, three rules — its overlay is the only one in the repo that has to *supply* hostnames, since the chart has no `ingress.domain`), `bulwark` 2, `stalwart` 2, `ytdlp-web-player` 2. The fail path was exercised rather than assumed: a Service renamed in the route, a port the Service does not expose, a port left out entirely, an emptied `parentRefs` with the chart's own guard disabled, an overlay that renders no route, a run with zero assertions, and — for the pairing — both the redirect rule deleted outright and the redirect pointed at a path other than the one stripped; each produced a `FAIL` naming both sides and a non-zero exit.
 
 ### Install-test (PR pipeline stage 2)