Initial commit — wiring diagram maker with full feature set

- FastAPI + SQLite backend with routers for diagrams, devices, wires,
  bundles, connectors, export, and Octopart/Nexar search
- Konva.js canvas: ortho/direct/curved routing, wire crossings, harness
  mode, snap-to-grid, multi-select, drag, resize, undo
- Wire features: color/stripe, twisted pair helix, shielded glow,
  gauge size label, multi-core bundle grouping, length/unit tracking
- Device library: connector, terminal block, cable, splice, label, group,
  relay, fuse, switch, component with custom connector support
- Exports: BOM CSV, assembly TXT, JSON, formboard layout, PNG image
- Auto-migration for schema changes via ALTER TABLE at startup

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

backend/app/database.py

@@ -0,0 +1,21 @@
+from sqlalchemy import create_engine
+from sqlalchemy.orm import sessionmaker, DeclarativeBase
+import os
+
+DB_PATH = os.path.join(os.path.dirname(__file__), "..", "wiring.db")
+DATABASE_URL = f"sqlite:///{os.path.normpath(DB_PATH)}"
+
+engine = create_engine(DATABASE_URL, connect_args={"check_same_thread": False})
+SessionLocal = sessionmaker(autocommit=False, autoflush=False, bind=engine)
+
+
+class Base(DeclarativeBase):
+    pass
+
+
+def get_db():
+    db = SessionLocal()
+    try:
+        yield db
+    finally:
+        db.close()