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/services/signal_history_service.py

@@ -0,0 +1,79 @@
+"""Signal history service -- time-bucketed signal strength queries.
+
+Uses raw SQL with TimescaleDB time_bucket() for efficient time-series aggregation.
+All queries run via the app_user engine (RLS enforced).
+"""
+
+import uuid
+
+from sqlalchemy import text
+from sqlalchemy.ext.asyncio import AsyncSession
+
+from app.schemas.site_alert import SignalHistoryPoint, SignalHistoryResponse
+
+# Mapping of range parameter to (time_bucket interval, lookback interval)
+RANGE_CONFIG = {
+    "24h": ("5 minutes", "24 hours"),
+    "7d": ("1 hour", "7 days"),
+    "30d": ("4 hours", "30 days"),
+}
+
+
+async def get_signal_history(
+    db: AsyncSession,
+    tenant_id: uuid.UUID,
+    device_id: uuid.UUID,
+    mac_address: str,
+    range: str = "7d",
+) -> SignalHistoryResponse:
+    """Query time-bucketed signal history for a specific client MAC on a device.
+
+    Args:
+        db: Database session (app_user with RLS).
+        tenant_id: Tenant UUID for RLS context.
+        device_id: Device UUID (the AP the client connects to).
+        mac_address: Client MAC address to query history for.
+        range: Time range -- "24h", "7d", or "30d".
+
+    Returns:
+        SignalHistoryResponse with time-bucketed signal avg/min/max.
+    """
+    bucket_interval, lookback = RANGE_CONFIG.get(range, RANGE_CONFIG["7d"])
+
+    result = await db.execute(
+        text(f"""
+            SELECT
+                time_bucket(:bucket_interval, wr.time) AS bucket,
+                avg(wr.signal_strength)::int AS signal_avg,
+                min(wr.signal_strength) AS signal_min,
+                max(wr.signal_strength) AS signal_max
+            FROM wireless_registrations wr
+            WHERE wr.mac_address = :mac_address
+              AND wr.device_id = :device_id
+              AND wr.tenant_id = :tenant_id
+              AND wr.time > now() - :lookback::interval
+              AND wr.signal_strength IS NOT NULL
+            GROUP BY bucket
+            ORDER BY bucket
+        """),
+        {
+            "bucket_interval": bucket_interval,
+            "lookback": lookback,
+            "mac_address": mac_address,
+            "device_id": str(device_id),
+            "tenant_id": str(tenant_id),
+        },
+    )
+    rows = result.fetchall()
+
+    items = [
+        SignalHistoryPoint(
+            timestamp=row.bucket,
+            signal_avg=row.signal_avg,
+            signal_min=row.signal_min,
+            signal_max=row.signal_max,
+        )
+        for row in rows
+    ]
+
+    return SignalHistoryResponse(items=items, mac_address=mac_address, range=range)