feat: Phase 0 walking skeleton — monorepo, API, web, ML stub

Sets up the full Phase 0 foundation:

- pnpm workspaces + turbo build graph; native module build approval
- packages/shared-types: HTTP contracts (Tip, Auth, Integrations, User)
- services/api: Express modular monolith with better-sqlite3/drizzle
  - auth: Google OAuth2 + PKCE via openid-client v6, cookie sessions
  - integrations: Todoist OAuth2 connect/disconnect, token vault
  - recommender: RandomPolicy over Todoist tasks, feedback sink
  - user: profile, consent capture, full account deletion (GDPR)
- apps/web: Next.js 15, three pages (sign-in → connect → tip)
  - tip page: black canvas, hold-to-act gesture, action sheet
  - PWA manifest + theme
- ml/serving: FastAPI stub implementing the POST /score contract
- infra: docker-compose (core/full profiles), Dockerfiles, CI skeleton
- .env.example with all required vars documented

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

turbo.json

@@ -0,0 +1,25 @@
+{
+  "$schema": "https://turbo.build/schema.json",
+  "ui": "tui",
+  "tasks": {
+    "build": {
+      "dependsOn": ["^build"],
+      "inputs": ["$TURBO_DEFAULT$", ".env*"],
+      "outputs": [".next/**", "!.next/cache/**", "dist/**"]
+    },
+    "dev": {
+      "cache": false,
+      "persistent": true
+    },
+    "type-check": {
+      "dependsOn": ["^build"]
+    },
+    "lint": {},
+    "test": {
+      "dependsOn": ["^build"]
+    },
+    "clean": {
+      "cache": false
+    }
+  }
+}