Default to power tier (unlimited) in dev when no subscription exists

Users without a subscription row in dev get power tier so rate limits
and quota checks don't block local development. In prod the fallback
remains free tier as before.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

app/billing/tier_manager.py

@@ -81,16 +81,18 @@ class TierManager:
     async def get_tier(self, user_id: str, db: AsyncSession) -> BillingTier:
         """Return the current billing tier for ``user_id`` from the DB.
 
-        Falls back to ``'free'`` when no subscription row exists.
+        Falls back to ``'power'`` in dev (unlimited) or ``'free'`` in prod
+        when no subscription row exists.
         """
         from app.models import Subscription  # noqa: PLC0415
+        from app.config.settings import settings  # noqa: PLC0415
 
         result = await db.execute(
             select(Subscription.tier).where(Subscription.user_id == user_id)
         )
         tier: str | None = result.scalar_one_or_none()
         if tier is None or tier not in FEATURES:
-            return "free"
+            return "power" if settings.ENV == "dev" else "free"
         return tier  # type: ignore[return-value]
 
     # ── Feature access ───────────────────────────────────────────────────