feat: add X-RateLimit response headers to throttle guard

[aniokedianne]

Closes #417
Closes #418
Closes #419
Closes #420

Update ThrottleGuard in src/common/guards/throttle.guard.ts to emit standard rate-limit response headers on every request:

Header	Value
X-RateLimit-Limit	Configured max requests per window (60)
X-RateLimit-Remaining	Requests remaining in the current window
X-RateLimit-Reset	Unix timestamp (seconds) when the window resets
Retry-After	Seconds until retry is allowed (429 responses only)

Headers are set in a private setRateLimitHeaders helper called on both the allow and deny paths, keeping the canActivate logic clean. The injected Response object comes from context.switchToHttp().getResponse<Response>() — no new dependencies required.

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