Backend: Add per-tenant feature flag service for staged rollout of new endpoints

[Baskarayelu]

Description

QuickLendX rolls out new endpoints (KYC tiers, dispute composer, bid ranking changes) but has no per-tenant flag. Today every API key sees the same routes regardless of stage. A simple sqlite-backed feature-flag service keyed by (api_key_id, flag) lets us roll out endpoints to a subset of customers without separate deployments. Distinct from the static OpenAPI versioning in #836.

Requirements and context

• Add backend/src/services/featureFlagService.ts reading from a feature_flags table.
• Add middleware backend/src/middleware/feature-flag.ts that 404s when a flag is off for the current API key.
• Provide admin endpoints to toggle flags.
• Document in backend/docs/admin-monitoring.md.

Suggested execution

Create branch feature/per-tenant-feature-flags:

• Add migration backend/src/migrations/v006_feature_flags.ts.
• Add backend/src/services/featureFlagService.ts and backend/src/middleware/feature-flag.ts.
• Add admin route in backend/src/routes/v1/admin.ts.
• Add backend/src/tests/feature-flag.test.ts.
• Update backend/docs/admin-monitoring.md.

Test and commit

Run npm test -- feature-flag. Cover: flag-on tenant sees endpoint, flag-off tenant 404s, default (no row) treats flag as off, admin toggle audited, cache invalidates on toggle. Confirm the flag check adds <1ms overhead.

Example commit message

feat: add per-tenant feature flag service for staged rollouts

Guidelines

• Minimum 95% test coverage
• Document flag administration in backend/docs/admin-monitoring.md
• Timeframe: 96 hours

[Miller070]

@Miller070 has applied to work on this issue as part of the Stellar Wave Program's 6th wave.

hey can i work here

ℹ️ Repo Maintainers: To accept this application, review their application or assign @Miller070 to this issue.

[Cjay-Cyber-2]

@Cjay-Cyber-2 has applied to work on this issue as part of the Stellar Wave Program's 6th wave.

I would like to get this issue

ℹ️ Repo Maintainers: To accept this application, review their application or assign @Cjay-Cyber-2 to this issue.

[grantfox-oss]

🦊 GrantFox — @Miller070 has been assigned to this issue as part of the Official Campaign campaign!

Next steps:

1. Open a Pull Request referencing this issue (e.g., Closes #1191)
2. Your PR will be reviewed by the QuickLendX maintainers

Good luck! Track your progress on GrantFox.

[drips-wave]

Congratulations, @Miller070! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on June 30, 2026.

🧑‍💻 @Miller070: Please resolve the issue such that the repo's maintainers have enough time to review your contribution before the due date. You'll earn Points for completing the issue on-time, which will make you eligible for a share of the Stellar Wave Program's reward pool.

Warning

When opening a PR, please link it to this issue to ensure it gets tracked accurately. Points are awarded when this issue is marked as completed by the maintainer.

🤠 Repo maintainers: Please keep an eye on the contributor's progress and review their work before the due date. You can manage this issue, including adjusting its complexity and points, here.

🌊 Happy Wave 🌊