Add Forgejo CI: ruff lint + pytest unit + gated image publish

Family-consistent CI for StashHandler (mirrors the NhenArchiver Python
sibling, minus the integration lane — StashHandler is SQLite-only with no
service containers).

- .forgejo/workflows/ci.yml: lint (ruff) -> unit (pytest) -> publish.
  publish builds + pushes git.fabledsword.com/bvandeusen/stashhandler with
  the family rule-46 tag scheme (dev->:dev+:c-<sha>, main->:latest+:c-<sha>,
  v* tag->:<version>+:latest). Gated on lint+unit. Needs REGISTRY_TOKEN.
- tests/: starter unit suite — hashing, SQLite dedup, media filter, transfer
  modes.
- pyproject.toml: ruff target + pytest pythonpath/testpaths.
- ci-requirements.md (family rule 39), .dockerignore.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_016nyYC9dTQ78SqhpNFtpMvT

.dockerignore

@@ -0,0 +1,20 @@
+# Keep the build context lean and the image free of dev/CI cruft.
+.git
+.gitignore
+.dockerignore
+.forgejo
+.claude
+tests
+pyproject.toml
+*.db
+*.db-wal
+*.db-shm
+__pycache__
+*.pyc
+.pytest_cache
+.venv
+README.md
+summary.md
+ci-requirements.md
+docker-compose.yaml
+docker-compose.prod.example.yaml