feat(stats): T32-T33 implement dashboard and usage endpoints

Add statistics router with two endpoints:
- GET /api/stats/dashboard: Aggregated dashboard statistics
  - Query param: days (1-365, default 30)
  - Auth required
  - Returns DashboardResponse

- GET /api/usage: Detailed usage statistics with filtering
  - Required params: start_date, end_date
  - Optional filters: api_key_id, model
  - Pagination: skip, limit (max 1000)
  - Auth required
  - Returns List[UsageStatsResponse]

Also add get_usage_stats() service function for querying
individual usage records with filtering and pagination.

src/openrouter_monitor/main.py

@@ -8,6 +8,7 @@ from fastapi.middleware.cors import CORSMiddleware
 from openrouter_monitor.config import get_settings
 from openrouter_monitor.routers import api_keys
 from openrouter_monitor.routers import auth
+from openrouter_monitor.routers import stats
 
 settings = get_settings()
 
@@ -31,6 +32,7 @@ app.add_middleware(
 # Include routers
 app.include_router(auth.router, prefix="/api/auth", tags=["authentication"])
 app.include_router(api_keys.router, prefix="/api/keys", tags=["api-keys"])
+app.include_router(stats.router)
 
 
 @app.get("/")

src/openrouter_monitor/routers/__init__.py

@@ -1,5 +1,6 @@
 """Routers package for OpenRouter Monitor."""
 from openrouter_monitor.routers import api_keys
 from openrouter_monitor.routers import auth
+from openrouter_monitor.routers import stats
 
-__all__ = ["auth", "api_keys"]
+__all__ = ["auth", "api_keys", "stats"]

src/openrouter_monitor/routers/stats.py

@@ -0,0 +1,118 @@
+"""Statistics router for OpenRouter API Key Monitor.
+
+T32-T33: Stats endpoints for dashboard and usage data.
+"""
+from datetime import date
+from typing import List, Optional
+
+from fastapi import APIRouter, Depends, Query, status
+from sqlalchemy.orm import Session
+
+from openrouter_monitor.database import get_db
+from openrouter_monitor.dependencies import get_current_user
+from openrouter_monitor.models import User
+from openrouter_monitor.schemas.stats import (
+    DashboardResponse,
+    UsageStatsResponse,
+)
+from openrouter_monitor.services.stats import (
+    get_dashboard_data,
+    get_usage_stats,
+)
+
+router = APIRouter(prefix="/api", tags=["statistics"])
+
+
+@router.get(
+    "/stats/dashboard",
+    response_model=DashboardResponse,
+    status_code=status.HTTP_200_OK,
+    summary="Get dashboard statistics",
+    description="Get aggregated statistics for the dashboard view.",
+)
+async def get_dashboard(
+    days: int = Query(
+        default=30,
+        ge=1,
+        le=365,
+        description="Number of days to look back (1-365)",
+    ),
+    db: Session = Depends(get_db),
+    current_user: User = Depends(get_current_user),
+) -> DashboardResponse:
+    """Get dashboard statistics for the current user.
+    
+    Args:
+        days: Number of days to look back (default 30, max 365)
+        db: Database session
+        current_user: Authenticated user
+        
+    Returns:
+        DashboardResponse with summary, by_model, by_date, and top_models
+    """
+    return get_dashboard_data(db, current_user.id, days)
+
+
+@router.get(
+    "/usage",
+    response_model=List[UsageStatsResponse],
+    status_code=status.HTTP_200_OK,
+    summary="Get detailed usage statistics",
+    description="Get detailed usage statistics with filtering and pagination.",
+)
+async def get_usage(
+    start_date: date = Query(
+        ...,
+        description="Start date for the query (YYYY-MM-DD)",
+    ),
+    end_date: date = Query(
+        ...,
+        description="End date for the query (YYYY-MM-DD)",
+    ),
+    api_key_id: Optional[int] = Query(
+        default=None,
+        description="Filter by specific API key ID",
+    ),
+    model: Optional[str] = Query(
+        default=None,
+        description="Filter by model name",
+    ),
+    skip: int = Query(
+        default=0,
+        ge=0,
+        description="Number of records to skip for pagination",
+    ),
+    limit: int = Query(
+        default=100,
+        ge=1,
+        le=1000,
+        description="Maximum number of records to return (1-1000)",
+    ),
+    db: Session = Depends(get_db),
+    current_user: User = Depends(get_current_user),
+) -> List[UsageStatsResponse]:
+    """Get detailed usage statistics with filtering.
+    
+    Args:
+        start_date: Start date for the query period (required)
+        end_date: End date for the query period (required)
+        api_key_id: Optional filter by API key ID
+        model: Optional filter by model name
+        skip: Number of records to skip (pagination)
+        limit: Maximum number of records to return
+        db: Database session
+        current_user: Authenticated user
+        
+    Returns:
+        List of UsageStatsResponse matching the filters
+    """
+    return get_usage_stats(
+        db=db,
+        user_id=current_user.id,
+        start_date=start_date,
+        end_date=end_date,
+        api_key_id=api_key_id,
+        model=model,
+        skip=skip,
+        limit=limit,
+    )

src/openrouter_monitor/services/stats.py

@@ -16,6 +16,7 @@ from openrouter_monitor.schemas.stats import (
     StatsByDate,
     StatsByModel,
     StatsSummary,
+    UsageStatsResponse,
 )
 
 
@@ -253,3 +254,61 @@ def get_dashboard_data(
         by_date=by_date,
         top_models=top_models,
     )
+
+
+def get_usage_stats(
+    db: Session,
+    user_id: int,
+    start_date: date,
+    end_date: date,
+    api_key_id: Optional[int] = None,
+    model: Optional[str] = None,
+    skip: int = 0,
+    limit: int = 100,
+) -> List[UsageStatsResponse]:
+    """Get detailed usage statistics with filtering.
+    
+    Args:
+        db: Database session
+        user_id: User ID to filter by
+        start_date: Start date for the query period
+        end_date: End date for the query period
+        api_key_id: Optional filter by API key ID
+        model: Optional filter by model name
+        skip: Number of records to skip (pagination)
+        limit: Maximum number of records to return
+        
+    Returns:
+        List of UsageStatsResponse matching the filters
+    """
+    from openrouter_monitor.models import UsageStats
+
+    # Build base query with join to ApiKey for user filtering
+    query = (
+        db.query(UsageStats)
+        .join(ApiKey, UsageStats.api_key_id == ApiKey.id)
+        .filter(ApiKey.user_id == user_id)
+        .filter(UsageStats.date >= start_date)
+        .filter(UsageStats.date <= end_date)
+    )
+
+    # Apply optional filters
+    if api_key_id is not None:
+        query = query.filter(UsageStats.api_key_id == api_key_id)
+
+    if model is not None:
+        query = query.filter(UsageStats.model == model)
+
+    # Apply ordering and pagination
+    results = (
+        query.order_by(UsageStats.date.desc(), UsageStats.model)
+        .offset(skip)
+        .limit(limit)
+        .all()
+    )
+
+    # Convert to response schema
+    return [
+        UsageStatsResponse.model_validate(record)
+        for record in results
+    ]