Request context propagation across HTTP, jobs, and DB layer (#213)

[Polliog]

Closes #213.

Summary

• New RequestContext primitive in @logtide/shared/context (AsyncLocalStorage-backed).
• Fastify plugin establishes context after auth resolves (org, project, user/apiKey, requestId, ip, ua).
• BullMQ producers transparently piggy-back _ctx on payloads; consumers wrap processors in context.run / runAsSystem.
• Backend pg.Pool.query and pool.connect() patched to prepend /* req=... */ SQL comments — visible in slow-query logs and pg_stat_activity.
• Reservoir engines (Timescale, ClickHouse, MongoDB) inject the same correlation in their native form (SQL comment / query_id / $comment).
• 7 worker cron callbacks wrapped in runAsSystem('cron:<name>').
• fetchWithContext helper for outbound HTTP (injects X-Logtide-Request-Id).

Out of scope

No callsite migration. Audit log / queue producers / webhook fetch keep their current argument-based form. Tracked as a follow-up.

Bonus fix

• apikeys: debounce last_used updates 60s per key — eliminates ~100 update/s on a single hot row under load. Pre-existing bug surfaced during validation.

Test plan

• Backend tests: 3941/3941 passing
• Shared: 31/31 passing
• Reservoir: Timescale 130/130, ClickHouse 57/57, MongoDB 35/35
• Integration test: HTTP -> producer -> consumer requestId correlation
• Smoke load test: 180/180 (5ms avg, 0% errors)
• Ingestion load test (5min sustained @ 100 req/s + burst): performance-equivalent to main (avg 568ms vs 590ms, error rate 0% vs 0.47%, P95 +7.8% within noise)

[codecov]

Codecov Report

❌ Patch coverage is 83.96739% with 59 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
...es/reservoir/src/engines/mongodb/mongodb-engine.ts	40.74%	32 Missing ⚠️
...eservoir/src/engines/timescale/timescale-engine.ts	87.09%	8 Missing ⚠️
packages/backend/src/database/connection.ts	85.10%	7 Missing ⚠️
...ervoir/src/engines/clickhouse/clickhouse-engine.ts	93.57%	7 Missing ⚠️
packages/backend/src/context/kysely-plugin.ts	80.95%	4 Missing ⚠️
packages/backend/src/context/bullmq-context.ts	96.77%	1 Missing ⚠️

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