* fix(aviation): stop Vercel from calling AviationStack directly
- get-airport-ops-summary: read from relay seed cache (aviation:delays:intl:v3)
instead of calling fetchAviationStackDelays() on every cache miss
- list-airport-flights + get-flight-status: proxy through Railway relay
/aviationstack endpoint instead of calling AviationStack from Vercel edge
- Add /aviationstack proxy endpoint to ais-relay with 2min in-memory cache
Vercel should NEVER call external paid APIs directly. Railway relay is
the sole egress point for AviationStack (gold standard).
* fix(config): update aviationStack feature to require WS_RELAY_URL
Aviation handlers now proxy through Railway relay instead of calling
AviationStack directly. Update runtime-config to reflect the actual
dependency.
e07bc8ede5