Fix double newsletter rate limiting policy mismatch

[hman38705]

Issue 007: Fix double newsletter rate limiting policy mismatch

Area: Backend
Priority: High
Files: services/api/src/main.rs, services/api/src/rate_limit.rs, services/api/src/handlers.rs

Problem

Middleware uses 5/hour while handler-level limiter uses 5/15min. Two conflicting policies create unpredictable throttling behavior.

Acceptance Criteria

• Single canonical rate limit policy is applied\n- No duplicate throttling paths exist\n- Docs and tests match the final policy\n- Policy is configurable via environment variable

[abore9769]

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Congratulations, @abore9769! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on April 29, 2026.

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This issue has been completed by @abore9769 as part of the Stellar Wave Program's 4th Wave 🥳

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