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>

.gitignore

@@ -0,0 +1,3 @@
+# https://dart.dev/guides/libraries/private-files
+# Created by `dart pub`
+.dart_tool/