Add budget module and push notifications for transactions

Budget: recurring items CRUD, yearly/monthly projections with no-double-count
logic, and full UI (overview, monthly detail, recurring items manager).

Push notifications: Web Push via VAPID keys, triggered on transaction creation
from n8n. Includes service worker handlers, frontend subscription flow, and
a test button on the Dashboard (temporary).

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

backend/app/api/v1/endpoints/transactions.py

@@ -7,8 +7,10 @@ from sqlmodel import Session, col, func, select
 
 from app.auth import get_current_user
 from app.db import get_session
+from app.api.v1.endpoints.notifications import send_push_to_all
 from app.models.models import (
     Category,
+    Currency,
     Transaction,
     TransactionCreate,
     TransactionRead,
@@ -55,6 +57,8 @@ def list_transactions(
     category_id: Optional[int] = None,
     cycle_year: Optional[int] = None,
     cycle_month: Optional[int] = None,
+    start_date: Optional[str] = None,
+    end_date: Optional[str] = None,
     limit: int = Query(default=50, le=500),
     offset: int = 0,
     session: Session = Depends(get_session),
@@ -70,6 +74,11 @@ def list_transactions(
     if cycle_year and cycle_month:
         start, end = get_cycle_range(cycle_year, cycle_month)
         query = query.where(Transaction.date >= start, Transaction.date < end)
+    elif start_date and end_date:
+        query = query.where(
+            Transaction.date >= datetime.fromisoformat(start_date),
+            Transaction.date < datetime.fromisoformat(end_date),
+        )
     query = query.order_by(col(Transaction.date).desc()).offset(offset).limit(limit)
     return session.exec(query).all()
 
@@ -170,6 +179,17 @@ def create_transaction(
     session.add(tx)
     session.commit()
     session.refresh(tx)
+
+    # Send push notification
+    symbol = "₡" if tx.currency == Currency.CRC else tx.currency.value
+    amount_str = f"{symbol}{tx.amount:,.0f}" if tx.currency == Currency.CRC else f"{symbol}{tx.amount:,.2f}"
+    send_push_to_all(
+        session,
+        title=f"💳 {tx.merchant}",
+        body=f"{amount_str} — {tx.bank.value} {tx.transaction_type.value.lower()}",
+        url=f"/budget",
+    )
+
     return tx