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/routers/diagrams.py

@@ -0,0 +1,53 @@
+from fastapi import APIRouter, Depends, HTTPException
+from sqlalchemy.orm import Session
+from typing import List
+from .. import models, schemas
+from ..database import get_db
+import datetime
+
+router = APIRouter(tags=["diagrams"])
+
+
+@router.get("/", response_model=List[schemas.DiagramSummary])
+def list_diagrams(db: Session = Depends(get_db)):
+    return db.query(models.Diagram).order_by(models.Diagram.updated_at.desc()).all()
+
+
+@router.post("/", response_model=schemas.DiagramSummary)
+def create_diagram(diagram: schemas.DiagramCreate, db: Session = Depends(get_db)):
+    db_diagram = models.Diagram(**diagram.model_dump())
+    db.add(db_diagram)
+    db.commit()
+    db.refresh(db_diagram)
+    return db_diagram
+
+
+@router.get("/{diagram_id}", response_model=schemas.DiagramFull)
+def get_diagram(diagram_id: int, db: Session = Depends(get_db)):
+    diagram = db.query(models.Diagram).filter(models.Diagram.id == diagram_id).first()
+    if not diagram:
+        raise HTTPException(status_code=404, detail="Diagram not found")
+    return diagram
+
+
+@router.patch("/{diagram_id}", response_model=schemas.DiagramSummary)
+def update_diagram(diagram_id: int, update: schemas.DiagramUpdate, db: Session = Depends(get_db)):
+    diagram = db.query(models.Diagram).filter(models.Diagram.id == diagram_id).first()
+    if not diagram:
+        raise HTTPException(status_code=404, detail="Diagram not found")
+    for key, value in update.model_dump(exclude_none=True).items():
+        setattr(diagram, key, value)
+    diagram.updated_at = datetime.datetime.utcnow()
+    db.commit()
+    db.refresh(diagram)
+    return diagram
+
+
+@router.delete("/{diagram_id}")
+def delete_diagram(diagram_id: int, db: Session = Depends(get_db)):
+    diagram = db.query(models.Diagram).filter(models.Diagram.id == diagram_id).first()
+    if not diagram:
+        raise HTTPException(status_code=404, detail="Diagram not found")
+    db.delete(diagram)
+    db.commit()
+    return {"ok": True}