Add Woodpecker CI pipeline with semantic versioning

Pipeline stages:
- restore: Restore NuGet dependencies
- build: Build in Release mode
- test: Run test suite
- version: Determine version from git tags
- package-nuget: Create NuGet package (main branch)
- package-docker: Build multi-arch Docker image (tags only)
- release: Create GitHub release with artifacts (tags only)

Versioning:
- Tags (v1.0.0) → version 1.0.0
- Main branch → version X.Y.Z-dev.main.abc1234
- PRs → version X.Y.Z-dev.branch.abc1234

Docker image published to ghcr.io/barryw/paperlessmcp

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

README.md

@@ -139,6 +139,25 @@ dotnet build        # Build
 dotnet test         # Run tests
 ```
 
+### CI/CD
+
+This project uses [Woodpecker CI](https://woodpecker-ci.org/) for continuous integration:
+
+| Event | Actions |
+|-------|---------|
+| **Push/PR** | Build → Test |
+| **Push to main** | Build → Test → Package NuGet |
+| **Tag (vX.Y.Z)** | Build → Test → Package → Docker → GitHub Release |
+
+**Versioning:** Semantic versioning via git tags. Create a release with:
+
+```bash
+git tag v1.0.0
+git push origin v1.0.0
+```
+
+**Docker Images:** `ghcr.io/barryw/paperlessmcp:latest`
+
 ### Project Structure
 
 ```