feat(ci): deploy to k3s straight from the pipeline (drop Flux plan)

Push to main = release: after build, a deploy job pins each app image to the
commit SHA (kustomize edit set image), kubectl-applies fleet/apps and waits
for the rollouts. The runner already runs in-cluster, so it reaches the API
server on the in-cluster service IP with a kubeconfig for the new ci-deployer
ServiceAccount (namespace-scoped admin, KUBECONFIG_B64 repo secret).

The drafted Flux sync/image-automation layer is removed — a GitOps controller
plus bot tag-bump commits is more machinery than a single-node cluster needs.
Sortable image tags and $imagepolicy markers go with it.

Also: per-router ACME-safe HTTP->HTTPS redirects for the app ingresses,
platform-api prod config completed (Authentik JWT/JWKS + admin API, Stalwart
via the cni0 gateway IP, OCIS/cold-storage placeholders until those tiers
exist) and the secrets template/README updated to match.

infrastructure/production/fleet/apps/platform-api.yaml

@@ -21,7 +21,8 @@ spec:
     spec:
       containers:
         - name: platform-api
-          # Pinned by CI to the commit SHA on release; :latest is dev-only.
+          # CI pins this to the commit SHA at deploy time (kustomize edit set image
+          # in .gitea/workflows/ci.yml); :latest here is the fallback.
           image: git.lastcloud.io/ronnibaslund/dezky/platform-api:latest
           imagePullPolicy: IfNotPresent
           ports: