feat: advanced features — dashboard, budgets, history, export

Backend:
- GET /api/v1/dashboard?month=YYYY-MM: KPIs, by_category, 6-month trend, budget alerts
- GET/POST/PUT/DELETE /api/v1/budgets: budget envelopes with spent_cents/remaining_cents
- POST /api/v1/budgets/rollover: copy budgets from M-1 to target month
- GET /api/v1/history?year=YYYY: monthly summary for the year
- GET /api/v1/export/csv|pdf?month=YYYY-MM: StreamingResponse exports (WeasyPrint PDF)
- New schemas: dashboard, budget, history
- Services: dashboard_service, budget_service
- Routers mounted in main.py

Frontend:
- DashboardPage: 4 KPI cards, PieChart (expenses by category), BarChart (6-month trend),
  month navigation, budget alert badges, CSV/PDF export buttons
- BudgetsPage: progress bars (green/orange/red), create/edit form, delete, rollover M-1
- HistoryPage: annual table with month click → dashboard, LineChart revenues/expenses
- CategoriesPage: list by type with create/edit/delete (was missing from Phase 2)
- TransactionsPage: added CSV/PDF export buttons
- App.tsx: full routing with ProtectedRoute + Layout for all authenticated pages
- New hooks: useDashboard, useBudgets (with mutations), useHistory
- API types + client updated for all new endpoints

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

backend/app/routers/history.py

@@ -0,0 +1,73 @@
+from datetime import date
+
+from fastapi import APIRouter, Depends, Query
+from sqlalchemy import func, select
+from sqlalchemy.ext.asyncio import AsyncSession
+
+from app.auth.dependencies import get_current_user
+from app.database import get_session
+from app.models.transaction import Transaction, TransactionType
+from app.models.user import User
+from app.schemas.history import HistoryResponse, MonthSummary
+from app.utils import utcnow
+
+router = APIRouter(prefix="/history", tags=["history"])
+
+
+@router.get("", response_model=HistoryResponse)
+async def get_history(
+    year: int = Query(default=None, description="Year (defaults to current year)"),
+    session: AsyncSession = Depends(get_session),
+    current_user: User = Depends(get_current_user),
+) -> HistoryResponse:
+    if year is None:
+        year = utcnow().year
+
+    months: list[MonthSummary] = []
+    for mon in range(1, 13):
+        start = date(year, mon, 1)
+        if mon == 12:
+            end = date(year + 1, 1, 1)
+        else:
+            end = date(year, mon + 1, 1)
+
+        result = await session.execute(
+            select(
+                func.coalesce(
+                    func.sum(
+                        func.case(
+                            (Transaction.type == TransactionType.income, Transaction.amount_cents),
+                            else_=0,
+                        )
+                    ),
+                    0,
+                ).label("income"),
+                func.coalesce(
+                    func.sum(
+                        func.case(
+                            (Transaction.type == TransactionType.expense, Transaction.amount_cents),
+                            else_=0,
+                        )
+                    ),
+                    0,
+                ).label("expense"),
+                func.count(Transaction.id).label("count"),
+            ).where(
+                Transaction.user_id == current_user.id,
+                Transaction.deleted_at.is_(None),
+                Transaction.transaction_date >= start,
+                Transaction.transaction_date < end,
+            )
+        )
+        row = result.one()
+        months.append(
+            MonthSummary(
+                month=f"{year}-{mon:02d}",
+                income_cents=row.income,
+                expense_cents=row.expense,
+                balance_cents=row.income - row.expense,
+                transaction_count=row.count,
+            )
+        )
+
+    return HistoryResponse(year=year, months=months)