Set up npm workspaces monorepo with Turborepo and local infra

Postgres and Redis run via docker compose on non-default ports (5447/6380)
to avoid clashing with other local services. React is pinned to a single
version across workspaces because Expo requires it.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01MzFywujuH9TiuXbr9vjoX8

.gitignore

@@ -0,0 +1,8 @@
+node_modules
+.env
+.env.local
+dist
+.next
+.turbo
+*.tsbuildinfo
+next-env.d.ts