Add release infrastructure and complete implementation

- Dockerfile: distroless container for MCP server
- GoReleaser: multi-platform binary and Docker builds with cosign signing
- GitHub Actions: release workflow using shared actions
- Semver config for automatic version calculation
- Persistence layer, content indexing, and improved tool handlers

Dockerfile

@@ -0,0 +1,3 @@
+FROM gcr.io/distroless/static-debian12:nonroot
+COPY compactor /usr/local/bin/compactor
+ENTRYPOINT ["compactor"]