feat: Phase 2H — void/waste log

Backend:
- New model: WasteLog (waste_log table) — product, quantity (float), reason, reason_notes,
  unit_cost_snapshot (copied at log time from product's effective cost), total_cost (stored),
  logged_by, business_day_id
- Cost snapshot: same logic as Phase 2A — breakdown sum first, fallback to cost_simple, null if neither
- New router /api/waste/:
  - GET / — list entries (?business_day_id= or ?from=&to=), ordered by logged_at desc
  - POST / — log waste; snapshots cost; attaches to open business day automatically
  - DELETE /{id} — manager only; only allowed within the same open business day
  - GET /summary — totals by reason + by product for a period
- product_performance report: waste_qty + waste_cost added per product from the same period;
  products with only waste (no sales) also included
- Migration: CREATE TABLE IF NOT EXISTS waste_log

Frontend:
- WastePage (/waste): fast log form (product picker, quantity, reason chips, notes);
  today's entries list below (scoped to active business day); cost shown per entry;
  delete button for today's entries; history section behind toggle with date-range picker
- ProductPerformance report: Απόβλητα column showing waste_qty + cost in amber
- Sidebar: Trash2 icon for Αποβλήτα (after Καρτέλες)

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

local_backend/routers/waste.py

@@ -0,0 +1,182 @@
+import json
+from fastapi import APIRouter, Depends, HTTPException, status, Query
+from sqlalchemy.orm import Session
+from typing import Optional
+
+from database import get_db
+from models.waste import WasteLog
+from models.product import Product
+from models.business_day import BusinessDay
+from models.user import User
+from schemas.waste import WasteLogCreate, WasteLogOut, VALID_REASONS, REASON_LABELS
+from routers.deps import require_manager
+
+router = APIRouter()
+
+
+def _effective_cost(product: Product) -> Optional[float]:
+    """Return product's current effective cost (breakdown sum or simple), or None."""
+    if product.cost_breakdown:
+        try:
+            entries = json.loads(product.cost_breakdown)
+            total = sum(e.get("amount", 0.0) for e in entries if isinstance(e, dict))
+            if total > 0:
+                return total
+        except Exception:
+            pass
+    if product.cost_simple:
+        return product.cost_simple
+    return None
+
+
+def _waste_out(w: WasteLog) -> dict:
+    product_name = w.product.name if w.product else f"#{w.product_id}"
+    logger_name = None
+    if w.logged_by:
+        logger_name = w.logged_by.full_name or w.logged_by.username
+    return {
+        "id": w.id,
+        "product_id": w.product_id,
+        "product_name": product_name,
+        "quantity": w.quantity,
+        "unit_cost_snapshot": w.unit_cost_snapshot,
+        "total_cost": w.total_cost,
+        "reason": w.reason,
+        "reason_label": REASON_LABELS.get(w.reason, w.reason),
+        "reason_notes": w.reason_notes,
+        "logged_by_id": w.logged_by_id,
+        "logged_by_name": logger_name,
+        "business_day_id": w.business_day_id,
+        "logged_at": w.logged_at,
+    }
+
+
+@router.get("/")
+def list_waste(
+    business_day_id: Optional[int] = None,
+    from_dt: Optional[str] = Query(default=None, alias="from"),
+    to_dt: Optional[str] = Query(default=None, alias="to"),
+    db: Session = Depends(get_db),
+    user: User = Depends(require_manager),
+):
+    from datetime import datetime
+    q = db.query(WasteLog).order_by(WasteLog.logged_at.desc())
+    if business_day_id:
+        q = q.filter(WasteLog.business_day_id == business_day_id)
+    elif from_dt and to_dt:
+        q = q.filter(
+            WasteLog.logged_at >= datetime.fromisoformat(from_dt),
+            WasteLog.logged_at <= datetime.fromisoformat(to_dt),
+        )
+    entries = q.all()
+    return {"entries": [_waste_out(w) for w in entries]}
+
+
+@router.post("/", status_code=status.HTTP_201_CREATED)
+def log_waste(
+    body: WasteLogCreate,
+    db: Session = Depends(get_db),
+    user: User = Depends(require_manager),
+):
+    if body.reason not in VALID_REASONS:
+        raise HTTPException(status_code=400, detail=f"Invalid reason. Valid: {sorted(VALID_REASONS)}")
+    if body.quantity <= 0:
+        raise HTTPException(status_code=400, detail="Quantity must be positive")
+
+    product = db.query(Product).filter(Product.id == body.product_id).first()
+    if not product:
+        raise HTTPException(status_code=404, detail="Product not found")
+
+    # Snapshot current effective cost
+    unit_cost = _effective_cost(product)
+    total_cost = round(unit_cost * body.quantity, 2) if unit_cost is not None else None
+
+    # Attach to open business day if any
+    active_day = db.query(BusinessDay).filter(BusinessDay.status == "open").first()
+
+    entry = WasteLog(
+        product_id=body.product_id,
+        quantity=body.quantity,
+        reason=body.reason,
+        reason_notes=body.reason_notes,
+        unit_cost_snapshot=unit_cost,
+        total_cost=total_cost,
+        logged_by_id=user.id,
+        business_day_id=active_day.id if active_day else None,
+    )
+    db.add(entry)
+    db.commit()
+    db.refresh(entry)
+    return _waste_out(entry)
+
+
+@router.delete("/{entry_id}", status_code=status.HTTP_204_NO_CONTENT)
+def delete_waste(
+    entry_id: int,
+    db: Session = Depends(get_db),
+    user: User = Depends(require_manager),
+):
+    entry = db.query(WasteLog).filter(WasteLog.id == entry_id).first()
+    if not entry:
+        raise HTTPException(status_code=404, detail="Waste entry not found")
+
+    # Only allow deletion within the same business day
+    active_day = db.query(BusinessDay).filter(BusinessDay.status == "open").first()
+    if active_day and entry.business_day_id != active_day.id:
+        raise HTTPException(status_code=403, detail="Can only delete waste entries from the current open business day")
+
+    db.delete(entry)
+    db.commit()
+
+
+@router.get("/summary")
+def waste_summary(
+    business_day_id: Optional[int] = None,
+    from_dt: Optional[str] = Query(default=None, alias="from"),
+    to_dt: Optional[str] = Query(default=None, alias="to"),
+    db: Session = Depends(get_db),
+    user: User = Depends(require_manager),
+):
+    from datetime import datetime
+    q = db.query(WasteLog)
+    if business_day_id:
+        q = q.filter(WasteLog.business_day_id == business_day_id)
+    elif from_dt and to_dt:
+        q = q.filter(
+            WasteLog.logged_at >= datetime.fromisoformat(from_dt),
+            WasteLog.logged_at <= datetime.fromisoformat(to_dt),
+        )
+    entries = q.all()
+
+    total_items = len(entries)
+    total_cost = round(sum(e.total_cost for e in entries if e.total_cost is not None), 2)
+    uncosted_count = sum(1 for e in entries if e.total_cost is None)
+
+    by_reason: dict = {}
+    by_product: dict = {}
+    for e in entries:
+        r = e.reason
+        if r not in by_reason:
+            by_reason[r] = {"reason": r, "label": REASON_LABELS.get(r, r), "count": 0, "total_cost": 0.0}
+        by_reason[r]["count"] += 1
+        by_reason[r]["total_cost"] += e.total_cost or 0.0
+
+        pid = e.product_id
+        pname = e.product.name if e.product else f"#{pid}"
+        if pid not in by_product:
+            by_product[pid] = {"product_id": pid, "product_name": pname, "qty": 0.0, "total_cost": 0.0}
+        by_product[pid]["qty"] += e.quantity
+        by_product[pid]["total_cost"] += e.total_cost or 0.0
+
+    for v in by_reason.values():
+        v["total_cost"] = round(v["total_cost"], 2)
+    for v in by_product.values():
+        v["total_cost"] = round(v["total_cost"], 2)
+
+    return {
+        "total_items": total_items,
+        "total_cost": total_cost,
+        "uncosted_count": uncosted_count,
+        "by_reason": sorted(by_reason.values(), key=lambda x: -x["count"]),
+        "by_product": sorted(by_product.values(), key=lambda x: -x["total_cost"]),
+    }