Implements `apps/gateway/src/bootstrap/tier-detector.ts` invoked from
`main.ts` before NestJS bootstraps. For each tier:
- `local`: no-op (PGlite is in-process)
- `standalone`: probe Postgres + Valkey
- `federated`: probe Postgres + Valkey + pgvector extension; reject
config upfront if `queue.type !== 'bullmq'`
Each probe has a 5-second hard cap and emits a structured
`TierDetectionError` with service / host / port / remediation. The
remediation field discriminates pgvector failure modes ("library not
available" vs "permission denied") so operators get actionable hints
without leaking credentials.
Adds `postgres` and `ioredis` as direct gateway deps; previously only
transitive. 12 unit tests cover happy paths and each fail-fast branch.
Refs #460
