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_test.go

@@ -0,0 +1,21 @@
+package buildinfo_test
+
+import (
+	"testing"
+
+	"kode.naiv.no/olemd/forgejo-mcp-broker/internal/buildinfo"
+)
+
+func TestDefaultsArePopulated(t *testing.T) {
+	// Build-info placeholders must never be empty: they are exposed on /healthz
+	// and an empty value would be observable to operators as a broken build.
+	if buildinfo.Version == "" {
+		t.Error("Version is empty")
+	}
+	if buildinfo.GitRevision == "" {
+		t.Error("GitRevision is empty")
+	}
+	if buildinfo.BuildDate == "" {
+		t.Error("BuildDate is empty")
+	}
+}