feat: microservices scaffold + Auth Service (Step 1)

- Add shared/ module: config, db, models, schemas, redis utilities
- Add Auth Service (services/auth/): register, login, refresh, me,
  ForwardAuth /verify endpoint for Traefik
- Add Traefik config: ACME/Cloudflare DNS-01, dynamic routing,
  ForwardAuth middleware, sticky sessions for WS Gateway
- Add service scaffolds: ws-gateway, chat, batch-agent, billing (READMEs)
- Add redis>=5.0.0 to requirements.txt
- Monolith app/ is untouched — strangler fig migration

services/auth/app/verify.py

@@ -0,0 +1,64 @@
+"""ForwardAuth verification endpoint for Traefik.
+
+Traefik calls GET /api/v1/auth/verify on every request to a protected
+service.  This endpoint validates the JWT from the Authorization header
+and returns identity headers that Traefik injects into downstream requests.
+
+Downstream services NEVER validate JWTs themselves — they trust the
+X-User-Id, X-User-Email, X-User-Tier headers injected by Traefik.
+"""
+
+from __future__ import annotations
+
+from fastapi import APIRouter, Request, Response
+from fastapi import status as http_status
+from jose import JWTError, jwt
+from sqlalchemy import select
+
+from shared.config import settings
+from shared.db import async_session
+from shared.models import Subscription
+
+router = APIRouter(tags=["auth"])
+
+
+@router.get("/auth/verify")
+async def verify(request: Request) -> Response:
+    """Validate JWT and return identity headers for Traefik ForwardAuth.
+
+    Returns 200 with X-User-* headers on success, 401 on failure.
+    Traefik copies response headers to the downstream request.
+    """
+    auth_header = request.headers.get("Authorization", "")
+    if not auth_header.startswith("Bearer "):
+        return Response(status_code=http_status.HTTP_401_UNAUTHORIZED)
+
+    token = auth_header[7:]  # strip "Bearer "
+
+    try:
+        payload = jwt.decode(
+            token, settings.JWT_SECRET, algorithms=[settings.JWT_ALGORITHM]
+        )
+        user_id: str | None = payload.get("sub")
+        email: str | None = payload.get("email")
+        if not user_id or not email:
+            return Response(status_code=http_status.HTTP_401_UNAUTHORIZED)
+    except JWTError:
+        return Response(status_code=http_status.HTTP_401_UNAUTHORIZED)
+
+    # Live tier lookup from subscriptions table
+    async with async_session() as db:
+        result = await db.execute(
+            select(Subscription.tier).where(Subscription.user_id == user_id)
+        )
+        default_tier = "power" if settings.ENV == "dev" else "free"
+        tier: str = result.scalar_one_or_none() or default_tier
+
+    return Response(
+        status_code=http_status.HTTP_200_OK,
+        headers={
+            "X-User-Id": user_id,
+            "X-User-Email": email,
+            "X-User-Tier": tier,
+        },
+    )