feat: bring repo up to REPO_POLICIES standards

- Create cmd/webhooker/main.go with fx dependency injection wiring
- Add REPO_POLICIES.md, .editorconfig, .dockerignore
- Add .gitea/workflows/check.yml for CI (docker build on push)
- Rewrite Makefile with all required targets (test, lint, fmt, fmt-check,
  check, build, hooks, docker, clean, dev, run, deps)
- Rewrite Dockerfile with sha256-pinned base images, golangci-lint
  installed from verified release archive, make check as build step
- Fix README.md: add required sections (description, getting started,
  rationale, design, TODO, license, author)
- Integrate TODO.md content into README.md and remove TODO.md
- Move config.yaml to configs/config.yaml.example
- Fix .gitignore pattern for webhooker binary
- Fix static/static.go embed directive (remove empty vendor dir)
- Fix database test to use in-memory config (no filesystem dependency)

closes #1
closes #2

.dockerignore

@@ -0,0 +1,15 @@
+.git/
+bin/
+*.md
+LICENSE
+.editorconfig
+.env
+.env.*
+*.db
+*.sqlite
+*.sqlite3
+.DS_Store
+.idea/
+.vscode/
+tmp/
+temp/