docs: initial planning artifacts for fjmcp-broker

Establish project scope, architecture, and phased implementation plan
for an OAuth 2.1 broker that fronts forgejo-mcp, delegating user
authentication to Forgejo and spawning a per-session stdio
forgejo-mcp subprocess scoped to each authenticated user's token.

No code yet — planning only.

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

.gitignore

@@ -0,0 +1,31 @@
+# Binaries
+/fjmcp-broker
+/dist/
+*.exe
+
+# Go build artifacts
+*.test
+*.out
+/vendor/
+
+# SQLite data files (broker token store)
+*.db
+*.db-journal
+*.db-wal
+*.db-shm
+/data/
+
+# Environment / secrets
+.env
+.env.local
+*.pem
+*.key
+
+# Editor / OS
+.idea/
+.vscode/
+.DS_Store
+*.swp
+
+# Logs
+*.log