feat: Phase 1 scaffold — frontend canvas + backend skeleton

Frontend:
- Vite + React 18 + TypeScript + Tailwind v4 + Shadcn/ui
- React Flow v12 canvas with all 11 node types and 5 edge types
- Dark theme with project design system (cyan, green, orange, purple accents)
- Collapsible sidebar, toolbar, detail panel
- Zustand store for canvas state
- Demo data with 10 nodes and 10 edges

Backend:
- FastAPI + SQLAlchemy async + SQLite (Python 3.13)
- DB models: Node, Edge, CanvasState, PendingDevice, ScanRun
- REST API routes: auth, nodes, edges, canvas, scan, status (WebSocket)
- JWT auth + bcrypt via config.yml
- Pydantic v2 schemas

Infra:
- GitHub Actions quality + security workflows
- .gitignore, .env.example, verify-tooling.sh, security-check.sh

backend/app/db/database.py

@@ -0,0 +1,25 @@
+from sqlalchemy.ext.asyncio import AsyncSession, async_sessionmaker, create_async_engine
+from sqlalchemy.orm import DeclarativeBase
+
+from app.core.config import settings
+
+engine = create_async_engine(
+    f"sqlite+aiosqlite:///{settings.sqlite_path}",
+    echo=False,
+)
+
+AsyncSessionLocal = async_sessionmaker(engine, class_=AsyncSession, expire_on_commit=False)
+
+
+class Base(DeclarativeBase):
+    pass
+
+
+async def init_db() -> None:
+    async with engine.begin() as conn:
+        await conn.run_sync(Base.metadata.create_all)
+
+
+async def get_db():
+    async with AsyncSessionLocal() as session:
+        yield session