chore: add CI/CD pipeline for Gitea deployment

- Add .gitea/workflows/build.yml for tag-triggered builds
- Add Dockerfile for containerized deployment (port 8086)
- Add .dockerignore to keep image lean
- Add CHANGELOG.md following Keep a Changelog format
- Update AGENTS.md with deployment verification URL

Build pipeline:
1. Create Gitea release on v* tag
2. Build and push Docker image to git.schweitz.internal
3. Trigger Watchtower for automatic deployment

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

AGENTS.md

@@ -48,6 +48,7 @@ When changes are ready for deployment:
 5. **CI/CD triggers automatically**:
    - Gitea CI builds Docker image on new version tag (starts with "v")
    - Watchtower pulls and deploys to production
+   - Verify deployment: `curl http://192.168.86.149:8086/health`
 
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