Initial scaffold: FocusFlow ADHD Task Manager backend

Dart Shelf API with modules: auth (JWT + PBKDF2), tasks (CRUD + dopamine scorer),
streaks (forgiveness + freeze), rewards (variable reward engine), time perception,
sync (offline-first push/pull), rooms (body doubling placeholder).
Includes DB migration (001_initial_schema.sql) and Docker Compose.

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

.env.example

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+# Server configuration
+PORT=8081
+APP_ENV=development  # development | staging | production
+
+# PostgreSQL connection string
+DATABASE_URL=postgresql://focusflow:focusflow@localhost:5433/focusflow
+
+# Redis connection string (for rate limiting, caching, sessions)
+REDIS_URL=redis://localhost:6380
+
+# JWT secret key — generate a strong random string for production
+JWT_SECRET=change-me-to-a-secure-random-string
+
+# JWT token lifetimes
+ACCESS_TOKEN_EXPIRY_MINUTES=15
+REFRESH_TOKEN_EXPIRY_DAYS=30
+
+# Rate limiting
+RATE_LIMIT_REQUESTS=100
+RATE_LIMIT_WINDOW_SECONDS=60
+
+# Logging level: ALL, FINEST, FINER, FINE, CONFIG, INFO, WARNING, SEVERE, SHOUT, OFF
+LOG_LEVEL=INFO