feat: add TWAP price calculation and caching service

[shogun444]

Summary

• Implemented TWAP calculation service across 1h, 4h, and 24h windows using prior-seed carry-forward price snapshots and graceful spot fallback for keys with 0 snapshots (src/modules/keys/key-twap.service.ts).
• Added Redis caching with window-matched TTLs (3600s, 14400s, 86400s) and automatic read-through on cache misses (src/constants/redis.constants.ts).
• Created 5-minute background computation job sweeping active keys with per-key error isolation, plus immediate backfill triggered on keyEventEmitter key registrations (src/jobs/twap-computation.job.ts).
• Added endpoint GET /keys/:keyId/price/twap?window=1h|4h|24h returning { twap, spotPrice, deltaPct, window, computedAt, stale }, flagging data as stale when older than 10 minutes (src/modules/keys/keys.routes.ts).
• Wired job start/stop lifecycle in src/server.ts and added TWAP_COMPUTATION_ENABLED / TWAP_COMPUTATION_INTERVAL_MINUTES to src/config.schema.ts and .env.example.

Testing

• pnpm lint
• pnpm build (passed on all new/touched files; full build has pre-existing Prisma/implicit-any errors)
• pnpm exec prisma generate when schema or generated types changed

Test results:

• pnpm test -- src/modules/keys/key-twap.service.test.ts src/jobs/twap-computation.job.test.ts --runInBand (2 suites, 15/15 passed)
• Regression suites: key-price-history, detect-price-movements, price-history-cleanup, config (4 suites, 19/19 passed)
• eslint and prettier clean on all touched files

Checklist

• Linked issue or backlog item (Closes Add TWAP price calculation and caching service for creator keys #963)
• No secrets or live credentials added
• Docs updated if setup or env changed (.env.example updated)
• Change is scoped to one problem

Closes #963

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