CI: migrate Docker build/push from Woodpecker to GitHub Actions

Was: Woodpecker built+pushed to DockerHub, then `kubectl set image` patched
the four Deployments to a pinned numeric tag. With Deployments pinned to
:51 (immutable tag), Keel polled forever and never saw a digest bump — and
no DockerHub pull-secret meant Keel hit 401 on the private repo at every
poll. The 4-Deployment setup also had a latent ImagePullBackOff risk: if a
node was replaced, fresh pulls would fail.

Now: GHA builds+pushes (.github/workflows/build-{api,frontend}.yml) on push
to master. Cluster Deployments reference :latest with an imagePullSecret
sourced from Vault via ESO (codified in infra/stacks/real-estate-crawler/
main.tf, separate commit). Keel polls :latest, sees the new digest after
each GHA build, and rolls all four Deployments.

- .github/workflows/build-api.yml: pytest (unit + integration/regression/
  e2e/test_listing_geojson) + buildx push viktorbarzin/realestatecrawler
  to {<8-char-sha>, latest}.
- .github/workflows/build-frontend.yml: vitest (all 4 ex-shards in one
  run) + Vite build with VITE_MAPBOX_TOKEN from GHA secret + buildx push
  viktorbarzin/immoweb to {<8-char-sha>, latest}.
- .woodpecker/{api,frontend}.yml renamed to
  .woodpecker/build-fallback-{api,frontend}.yml with `event: deployment`
  so they no longer fire on push — kept as manual-only fallback if GHA
  is down (CLAUDE.md convention from the 10 already-migrated projects).
- .claude/CLAUDE.md: Git Workflow section updated to reflect GHA as
  primary + the dockerhub-pull-secret wiring.

GHA repo secrets DOCKERHUB_TOKEN and MAPBOX_TOKEN populated from Vault
fields viktor.dockerhub_registry_password and ci/global.wrongmove-mapbox-token
respectively (DOCKERHUB_USERNAME=viktorbarzin was already set).

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

.woodpecker/build-fallback-api.yml

@@ -1,6 +1,10 @@
+# Fallback pipeline — only fires on manual `deployment` event after GHA
+# (.github/workflows/build-api.yml) became the primary builder on
+# 2026-05-18. Kept around in case GHA is down and a build needs to ship
+# from inside the cluster. `event: deployment` means it never auto-fires
+# on push.
 when:
-  - event: push
-    branch: master
+  - event: deployment
 
 clone:
   git:

.woodpecker/build-fallback-frontend.yml

@@ -1,6 +1,10 @@
+# Fallback pipeline — only fires on manual `deployment` event after GHA
+# (.github/workflows/build-frontend.yml) became the primary builder on
+# 2026-05-18. Kept around in case GHA is down and a build needs to ship
+# from inside the cluster. `event: deployment` means it never auto-fires
+# on push.
 when:
-  - event: push
-    branch: master
+  - event: deployment
 
 clone:
   git: