Feat: Frontend-Overhaul E — Lane-Editor, Routing-Policy (hot-reload) & Latenz-Karte

Teil 1: VoiceLatencyCard auf dem Dashboard (GET /api/voice/metrics, C2) —
zeigt STT/Vision/Chat-TTFB/TTS mit p50/p95/last + count.

Teil 2: UI-editierbare Routing-Policy. Neuer routing_policy.py (hot-reload JSON
unter MODELS_DIR/mc2-routing.json, Env=Defaults, atomarer Write, Validierung).
router_logic, gateway_proxy und gateway.routing_summary lesen jetzt live via
load_policy(); routing_summary ist lane-bewusst (chat/coding statt altem auto).
Neue Endpoints GET/PUT /api/routing/policy.

Teil 3: LaneEditor.tsx als ZONE im Cockpit (chat/coding-Aliase + Schwellen +
fast_no_think, Speichern/Default-je-Feld); Gateway-Node zeigt die Lanes.

Verifiziert: npm run build (tsc strict) clean, FastAPI TestClient (GET/PUT,
Validierung, Persistenz, Hot-reload durch die API), venv-Smoke (Routing).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

backend/routers/routing.py

@@ -1,8 +1,10 @@
-"""Routing-Endpoint: zeigt den eingebauten Gateway (model:auto fast↔heavy)."""
+"""Routing-Endpoints: Lane-Summary (chat/coding) + UI-editierbare Policy (hot-reload)."""
 
-from fastapi import APIRouter
+from fastapi import APIRouter, HTTPException
+from pydantic import BaseModel
 
 from services import gateway
+from services.routing_policy import policy_meta, save_policy
 
 router = APIRouter(prefix="/api")
 
@@ -10,3 +12,32 @@ router = APIRouter(prefix="/api")
 @router.get("/routing")
 def routing() -> dict:
     return {**gateway.routing_summary(), "gateway_reachable": gateway.gateway_reachable()}
+
+
+@router.get("/routing/policy")
+def get_policy() -> dict:
+    """Aktuelle Policy + Defaults (für „Zurücksetzen“) + Feld-Spezifikation für den Editor."""
+    return policy_meta()
+
+
+class PolicyPatch(BaseModel):
+    fast: str | None = None
+    heavy: str | None = None
+    coder: str | None = None
+    coder_lite: str | None = None
+    heavy_chars: int | None = None
+    coding_escalate_chars: int | None = None
+    fast_no_think: bool | None = None
+
+
+@router.put("/routing/policy")
+def put_policy(patch: PolicyPatch) -> dict:
+    """Teil-Update der Routing-Policy. Validiert, persistiert atomar, sofort wirksam (hot-reload)."""
+    fields = {k: v for k, v in patch.model_dump().items() if v is not None}
+    if not fields:
+        raise HTTPException(status_code=400, detail="Keine Felder zum Aktualisieren.")
+    try:
+        new_policy = save_policy(fields)
+    except (ValueError, TypeError) as e:
+        raise HTTPException(status_code=400, detail=f"Ungültige Policy: {e}")
+    return {"policy": new_policy}