Feature/issue 045 fingerprint ratelimit

[ugoocreates-pixel]

Closes #619

This PR addresses backend issue [b#045] by implementing a per-user token-bucket rate limit for the /api/fingerprint endpoint. This ensures that we prevent abuse or excessive polling on the fingerprint route while returning a standard 429 Too Many Requests along with a Retry-After header when the limit is exceeded.

Changes Made

• Environment Configuration (src/config/env-schema.ts): Added configurable rate limit parameters FINGERPRINT_RATE_LIMIT_CAPACITY (default 60) and FINGERPRINT_RATE_LIMIT_WINDOW_MS (default 60,000 ms).
• Rate Limit Middleware (src/middleware/rateLimit.ts): Exported a pre-configured fingerprintRateLimiter utilizing createPerUserTokenBucketLimiter.
• Route Update (src/routes/fingerprint.ts): Injected the rate limit middleware into the GET /api/fingerprint route.
• Testing (tests/fingerprint.test.ts): Added an integration test that isolates an IP and exhausts the rate limit to verify that the 61st request correctly returns a 429 status code, the appropriate error code payload (rate_limit_exceeded), and the Retry-After header.

Validation & Guidelines

• ✅ Minimum 90% test coverage on changed lines.
• ✅ Uses standard project error envelope ({ error: { code, ... } }).
• ✅ Incorporates structured logging with context and correlation IDs (handled seamlessly by the rate limit middleware wrapper).
• ✅ Clean documentation/inline comments where applicable.

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[greatest0fallt1me]

Merging — thanks for staying scoped to the issue!