docs(versioning): define release policy and close MVP0 pipeline tasks

VERSIONING.md

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+# Versioning Policy
+
+## Source Of Truth
+
+- Canonical version: root `package.json` field `version`
+- Tag format: `vX.Y.Z`
+
+Tag validation is enforced in CI:
+
+- `.gitea/scripts/validate-tag-version.sh`
+
+## SemVer Strategy
+
+- `major`: breaking API/behavior changes
+- `minor`: backward-compatible features
+- `patch`: backward-compatible fixes
+
+## Build Metadata Policy
+
+Use git metadata in runtime display format:
+
+- `<version>+sha.<short>`
+
+Example:
+
+- `0.1.0+sha.a1b2c3d`
+
+## Footer Display Plan (Admin + Web)
+
+Planned runtime footer fields:
+
+- app name
+- version from root `package.json`
+- commit hash (short)
+- environment (`dev|staging|production`)
+
+Implementation note:
+
+- inject values at build/deploy time through env vars
+- render in shared footer components
+
+## CI Version Injection
+
+Release/deploy workflows pass release tag and commit metadata:
+
+- `.gitea/workflows/release.yml`
+- `.gitea/workflows/deploy.yml`
+
+Required inputs:
+
+- release tag (`vX.Y.Z`)
+- image tag for deployment
+
+## Validation Strategy
+
+CI validations:
+
+- tag equals `v${package.json.version}`
+- required checks pass before release builds
+
+Runtime validations (planned):
+
+- smoke tests assert footer version/hash format
+- environment-specific deployment checks assert expected image tag
+
+## Changelog and Release Publication
+
+- changelog generation command:
+  - `bun run changelog:release`
+- release workflow generates changelog on tag pipeline
+- release notes publication remains a dedicated step in CI workflow.