Add BQL-based report endpoints for expenses and contributions

New endpoints:
- GET /api/v1/reports/expenses - Expense summary by account or month
- GET /api/v1/reports/contributions - User contribution totals

New FavaClient methods:
- get_expense_summary_bql() - Aggregates expenses with date filtering
- get_user_contributions_bql() - Aggregates user expense submissions

Both use sum(weight) for efficient SATS aggregation from price notation.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

views_api.py

@@ -2215,6 +2215,135 @@ async def api_get_castle_users(
     return users
 
 
+@castle_api_router.get("/api/v1/reports/expenses")
+async def api_expense_report(
+    start_date: Optional[str] = None,
+    end_date: Optional[str] = None,
+    group_by: str = "account",
+    wallet: WalletTypeInfo = Depends(require_admin_key),
+) -> dict:
+    """
+    Get expense summary report using BQL.
+
+    Args:
+        start_date: Filter from this date (YYYY-MM-DD), optional
+        end_date: Filter to this date (YYYY-MM-DD), optional
+        group_by: "account" (by expense category) or "month" (by month)
+
+    Returns:
+        {
+            "summary": [
+                {"account": "Expenses:Supplies:Food", "fiat": 500.00, "sats": 550000},
+                ...
+            ],
+            "total_fiat": 1500.00,
+            "total_sats": 1650000,
+            "fiat_currency": "EUR",
+            "group_by": "account",
+            "start_date": "2025-01-01",
+            "end_date": "2025-12-31"
+        }
+
+    Admin only.
+    """
+    from .fava_client import get_fava_client
+
+    if group_by not in ["account", "month"]:
+        raise HTTPException(
+            status_code=HTTPStatus.BAD_REQUEST,
+            detail="group_by must be 'account' or 'month'"
+        )
+
+    fava = get_fava_client()
+    summaries = await fava.get_expense_summary_bql(
+        start_date=start_date,
+        end_date=end_date,
+        group_by=group_by
+    )
+
+    # Calculate totals
+    total_fiat = sum(s.get("fiat", 0) for s in summaries)
+    total_sats = sum(s.get("sats", 0) for s in summaries)
+
+    return {
+        "summary": summaries,
+        "total_fiat": total_fiat,
+        "total_sats": total_sats,
+        "fiat_currency": "EUR",
+        "group_by": group_by,
+        "start_date": start_date,
+        "end_date": end_date,
+        "count": len(summaries)
+    }
+
+
+@castle_api_router.get("/api/v1/reports/contributions")
+async def api_contributions_report(
+    wallet: WalletTypeInfo = Depends(require_admin_key),
+) -> dict:
+    """
+    Get user contribution report using BQL.
+
+    Shows total expenses submitted by each user (creating payables).
+
+    Returns:
+        {
+            "contributions": [
+                {
+                    "user_id": "cfe378b3",
+                    "username": "alice",
+                    "total_fiat": 1500.00,
+                    "total_sats": 1650000,
+                    "entry_count": 25
+                },
+                ...
+            ],
+            "total_fiat": 5000.00,
+            "total_sats": 5500000,
+            "fiat_currency": "EUR",
+            "user_count": 5
+        }
+
+    Admin only.
+    """
+    from lnbits.core.crud.users import get_user
+    from .fava_client import get_fava_client
+
+    fava = get_fava_client()
+    contributions = await fava.get_user_contributions_bql()
+
+    # Enrich with usernames
+    for contrib in contributions:
+        user_id = contrib["user_id"]
+        # Try to find full user_id from wallet settings
+        settings = await get_all_user_wallet_settings()
+        full_user_id = None
+        for s in settings:
+            if s.id.startswith(user_id):
+                full_user_id = s.id
+                break
+
+        if full_user_id:
+            user = await get_user(full_user_id)
+            contrib["username"] = user.username if user and user.username else None
+            contrib["full_user_id"] = full_user_id
+        else:
+            contrib["username"] = None
+            contrib["full_user_id"] = None
+
+    # Calculate totals
+    total_fiat = sum(c.get("total_fiat", 0) for c in contributions)
+    total_sats = sum(c.get("total_sats", 0) for c in contributions)
+
+    return {
+        "contributions": contributions,
+        "total_fiat": total_fiat,
+        "total_sats": total_sats,
+        "fiat_currency": "EUR",
+        "user_count": len(contributions)
+    }
+
+
 @castle_api_router.get("/api/v1/users/{user_id}/unsettled-entries")
 async def api_get_unsettled_entries(
     user_id: str,