Initial commit: webmail client (M0/M1)

Three-pane webmail client.
- Backend: FastAPI + async SQLAlchemy + arq worker (Postgres/Redis), IMAP/SMTP
  sync, threading, search, drafts/outbox with undo, attachments, 2FA.
- Frontend: React 18 + Vite + TypeScript + TanStack Query + Tailwind; three-pane
  UI with rich-text composer, light/dark themes, resizable panels.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Makefile

@@ -0,0 +1,19 @@
+up:        ## start services
+	docker compose -f docker/docker-compose.yml up -d postgres redis meilisearch
+down:      ## stop services (data kept)
+	docker compose -f docker/docker-compose.yml down
+reset-db:  ## DESTRUCTIVE: wipe db + search + blobs, re-migrate
+	docker compose -f docker/docker-compose.yml down -v
+	rm -rf var/blobs && mkdir -p var/blobs
+	docker compose -f docker/docker-compose.yml up -d --wait postgres redis meilisearch
+	cd backend && alembic upgrade head
+api:
+	uvicorn app.main:create_app --factory --reload --port 8000 --app-dir backend
+worker:
+	cd backend && arq workers.worker.WorkerSettings
+web:
+	cd frontend && npm run dev
+test:
+	cd backend && pytest -q && cd ../frontend && npx vitest run
+mail-test:  ## start throwaway IMAP/SMTP server
+	docker compose -f docker/docker-compose.yml up -d greenmail