feat(15-01): add signal history and site alert services, routers, and main.py wiring

- Create signal_history_service with TimescaleDB time_bucket queries for 24h/7d/30d ranges
- Create site_alert_service with full CRUD for rules, events list/resolve, and active count
- Create signal_history router with GET endpoint for time-bucketed signal data
- Create site_alerts router with CRUD endpoints for rules and event management
- Wire both routers into main.py with /api prefix

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

backend/app/routers/signal_history.py

@@ -0,0 +1,52 @@
+"""
+Signal history API endpoint.
+
+Routes: /api/tenants/{tenant_id}/devices/{device_id}/signal-history
+
+RBAC:
+- viewer: GET (read-only)
+"""
+
+import uuid
+
+from fastapi import APIRouter, Depends, HTTPException, Query, status
+from sqlalchemy.ext.asyncio import AsyncSession
+
+from app.database import get_db
+from app.middleware.tenant_context import CurrentUser, get_current_user
+from app.routers.devices import _check_tenant_access
+from app.schemas.site_alert import SignalHistoryResponse
+from app.services import signal_history_service
+
+router = APIRouter(tags=["signal-history"])
+
+
+@router.get(
+    "/tenants/{tenant_id}/devices/{device_id}/signal-history",
+    response_model=SignalHistoryResponse,
+    summary="Get signal strength history for a wireless client",
+)
+async def get_signal_history(
+    tenant_id: uuid.UUID,
+    device_id: uuid.UUID,
+    mac_address: str = Query(..., description="Client MAC address to query history for"),
+    range: str = Query("7d", description="Time range: 24h, 7d, or 30d"),
+    current_user: CurrentUser = Depends(get_current_user),
+    db: AsyncSession = Depends(get_db),
+) -> SignalHistoryResponse:
+    """Get time-bucketed signal strength history for a wireless client on a device."""
+    await _check_tenant_access(current_user, tenant_id, db)
+
+    if range not in ("24h", "7d", "30d"):
+        raise HTTPException(
+            status_code=status.HTTP_400_BAD_REQUEST,
+            detail="range must be one of: 24h, 7d, 30d",
+        )
+
+    return await signal_history_service.get_signal_history(
+        db=db,
+        tenant_id=tenant_id,
+        device_id=device_id,
+        mac_address=mac_address,
+        range=range,
+    )