security: enforce strict CSP in production middleware

[nanaf6203-bit]

Summary

src/middleware.ts references CSP_ENFORCE env flag but there is no observable test for the strict CSP.

Affected area

src/middleware.ts, src/app/api/csp-report/route.ts

Steps to reproduce / impact

Without a strict CSP, XSS payloads (covered by #13, #22, #23) become viable. CSP is the second line of defence.

Expected behaviour

Publish a baseline CSP (default-src 'self'; img-src 'self' data: ipfs:; script-src 'self' 'nonce-…'), enforce in production, and report-only in non-prod.

Acceptance criteria

• Document CSP.
• Add a Playwright test verifying CSP blocks inline scripts.
• Add CSP report-only in dev and confirm reports land.

[sandrawillow001-afk]

@sandrawillow001-afk has applied to work on this issue as part of the Stellar Wave Program's 6th wave.

i can work on this sir

ℹ️ Repo Maintainers: To accept this application, review their application or assign @sandrawillow001-afk to this issue.

[drips-wave]

Congratulations, @sandrawillow001-afk! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on June 30, 2026.

🧑‍💻 @sandrawillow001-afk: 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 🌊

[drips-wave]

This issue has been completed by @sandrawillow001-afk as part of the Stellar Wave Program's 6th Wave 🥳

😎 @sandrawillow001-afk: You earned 200 Points for completing this issue! After the current Wave ends, you'll be eligible for a percentage of the Wave's reward pool based on the percentage of total points you've earned. Learn more here. You can also Leave a review to share your experience working on this issue.

🧑‍💻 Repo maintainers: How'd the contributor do? Leave a review to share your experience working with them.