urlaubsverwaltung: NOTES.txt and the exponential-quantity fix (8.1.0+up6.7.0)

Teil von #157 und Teil von #43.

#157: multiplyQuantity turned a bare byte count into exponential notation.
Values pass through fromYaml, which parses every number as float64, and Go's
"%v" switches float64 to exponential notation from about 1e6 upwards. Both
places that stringify a number now go through the new formatNumber helper -
the input of multiplyQuantity, which aborted the render with an unsupported
suffix "e+06", and the output of a non-integer product, which did not abort
at all but rendered an invalid quantity that only the API server rejects.

Measured on this chart against ci/urlaubsverwaltung/test-values.yaml:

  requests.memory=1048576              before: abort, suffix "e+06"
                                       after:  request 1048576, limit "3145728"
  requests.ephemeralStorage=2097152    before: abort, suffix "e+06"
                                       after:  limit "6291456"
  memory=999999, limitFactor=1.5       before: limit "1.4999985e+06", no abort
                                       after:  limit "1499998.5"
  requests.memory=65536 (regression)   196608 before and after

The correction is the canonical one, word for word as merged into
template-chart, voucher-vault and zipline; only the helper prefix differs.
urlaubsverwaltung has a single resources path and a single render site
(the Deployment), and both were verified.

#43: adds a NOTES.txt. Its content was verified against a running release in
a throwaway k3d cluster rather than taken from upstream documentation - the
identity provider being resolved at boot (a bad issuer-uri crashlooops the
pod instead of breaking the login), the buildpack sizing the JVM heap from
the computed memory limit, /actuator/health answering 503 for the lifetime of
the release because the chart points the mail sender at localhost:1025, the
probe groups not reacting to a database outage, and a name collision in
urlaubsverwaltung.env making the next helm upgrade fail on the patch order.

README.md is deliberately untouched: the line listing the charts that ship a
NOTES.txt collides with every parallel NOTES PR and is pulled up once at the
end of the programme.

Minor bump: a NOTES.txt renders no Kubernetes object and the quantity fix
changes no default. appVersion unchanged.

urlaubsverwaltung/templates/_helpers.tpl

@@ -67,7 +67,7 @@ Handles plain numbers ("2", "0.5", 1073741824), decimal ("1.5Gi"), binary
 results are printed without a decimal point.
 */}}
 {{- define "urlaubsverwaltung.multiplyQuantity" -}}
-{{- $quantity := printf "%v" .quantity -}}
+{{- $quantity := include "urlaubsverwaltung.formatNumber" .quantity -}}
 {{- $number := regexFind "^[0-9]+(\\.[0-9]+)?" $quantity -}}
 {{- if not $number -}}
 {{- fail (printf "cannot parse resource quantity %q" $quantity) -}}
@@ -80,7 +80,24 @@ results are printed without a decimal point.
 {{- if eq $product (floor $product) -}}
 {{- printf "%d%s" (int64 $product) $suffix -}}
 {{- else -}}
-{{- printf "%v%s" $product $suffix -}}
+{{- printf "%s%s" (include "urlaubsverwaltung.formatNumber" $product) $suffix -}}
+{{- end -}}
+{{- end -}}
+
+{{/*
+Render a number as a plain decimal string, never in exponential notation.
+
+Why this exists (issue #157): the null-safe fallback helpers pass values
+through fromYaml, which parses every number as float64. Go's "%v" switches
+float64 to exponential notation from about 1e6 upwards, so a bare byte count
+like 1048576 became "1.048576e+06" - not a valid Kubernetes quantity, and the
+render aborted. Strings ("512Mi") are passed through untouched.
+*/}}
+{{- define "urlaubsverwaltung.formatNumber" -}}
+{{- if kindIs "float64" . -}}
+{{- regexReplaceAll "\\.?0+$" (printf "%.10f" .) "" -}}
+{{- else -}}
+{{- printf "%v" . -}}
 {{- end -}}
 {{- end -}}