feat: bootstrap Go project layout (forgejo-mcp-broker-n84)

- Initialize go.mod with module path kode.naiv.no/olemd/forgejo-mcp-broker
- Create directory layout: cmd/broker + internal/{buildinfo,config,log,store,httpserver}
- Add Makefile with build/test/lint/tidy/clean targets and ldflags-injected build info
- Stub cmd/broker/main.go with --version support; real wiring follows in -t37
- Stub doc.go for each internal/* package, pointing to the issue that fills it in

Closes forgejo-mcp-broker-n84.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

internal/buildinfo/buildinfo.go

@@ -0,0 +1,12 @@
+// Package buildinfo exposes compile-time build metadata.
+//
+// Values are injected at link time via -ldflags -X (see the Makefile). When
+// the binary is built without those flags (e.g. go run, go test), the
+// placeholder defaults below are used.
+package buildinfo
+
+var (
+	Version     = "dev"
+	GitRevision = "unknown"
+	BuildDate   = "unknown"
+)