ci: align Gitea CI/CD + Docker with the notify-bridge template

Adopt the proven notify-bridge pipeline pattern and fix deployment bugs.

Workflows:
- build.yml: split into parallel frontend / backend / build-image jobs.
  Run svelte-check + vitest + `go vet ./...` + `go test ./internal/...`
  (tests were never executed in CI). Use buildx with GHA layer cache and
  pin Go to 1.25. Quote the `if:` skip-guard so it is valid YAML.
- release.yml: gate the release on a passing test job, then build & push
  the image, then create the Gitea release LAST so a failed image build
  can no longer leave an orphan release. Use buildx + registry buildcache,
  a hard registry login (a push failure now fails the release), and
  auto-generate a changelog between tags.

Docker:
- Dockerfile: pin golang to 1.25 (matches go.mod's `go 1.25.0`), add
  BuildKit cache mounts for the module + build caches, an OCI source
  label, VOLUME /app/data, and a HEALTHCHECK on /readyz.
- docker-compose.yml: fix the healthcheck — it targeted POST-only
  /api/auth/login (405 -> always unhealthy); now /readyz. Point the image
  name at the Gitea registry tag with build-from-source as the default.
- .dockerignore: exclude ~95 MB of stray binaries, logs, env, and CI/doc
  files from the build context.

.dockerignore

@@ -1,9 +1,47 @@
+# VCS / tooling
 .git
-node_modules
-web/node_modules
-web/build
-data
-*.md
-plans/
-.claude/
+.gitignore
 .dockerignore
+.gitea/
+.github/
+.claude/
+.code-review-graph/
+.vex.toml
+.facts-sync.json
+.facts-suggestions.md
+
+# Node / frontend build artifacts (frontend stage rebuilds web/build)
+node_modules/
+web/node_modules/
+web/build/
+web/.svelte-kit/
+
+# Runtime / local data
+data/
+.env
+.env.*
+*.log
+
+# Compiled binaries (rebuilt inside the image)
+tinyforge
+tinyforge.exe
+tinyforge-server.exe
+server.exe
+docker-watcher
+docker-watcher.exe
+docker-watcher.exe~
+/cli
+/cli.exe
+
+# Build/orchestration files not needed inside the image
+Dockerfile
+docker-compose.yml
+Makefile
+*.example.yaml
+
+# Docs / planning / design (not needed at runtime)
+*.md
+docs/
+plans/
+design-mockups/
+test-data/