test(refresh-rate-limiter): add coverage for IP throttling and window reset behavior (JhaSourav07#3161)

## Description

Adds a complete test suite for services/github/refresh-rate-limiter.ts
to validate refresh request throttling, cooldown window expiration,
environment-based configuration, and response metadata.

This ensures the rate limiter continues to protect manual refresh
endpoints from excessive usage while remaining configurable through
environment variables.

## Changes
Added
services/github/refresh-rate-limiter.test.ts
Test Coverage

Implemented 5 unit tests covering:

- Initial refresh requests are allowed for a new IP.
- Requests are blocked after the configured limit is reached.
- Rate limits automatically reset after the cooldown window expires.
- Reset timestamps and remaining request counts are calculated
correctly.
- MAX_REFRESHES_PER_HOUR environment variable overrides the default
configuration


Fixes JhaSourav07#2297 

## Pillar

- [x] 📐 Pillar 2 — Geometric SVG Improvement
- [x] 🕐 Pillar 3 — Timezone Logic Optimization


## Checklist before requesting a review:

- [x] I have read the `CONTRIBUTING.md` file.
- [x] I have tested these changes locally
(`localhost:3000/api/streak?user=YOUR_USERNAME`).
- [x] I have run `npm run format` and `npm run lint` locally and
resolved all errors (CI will fail otherwise).
- [x] My commits follow the Conventional Commits format (e.g.,
`feat(themes): ...`, `fix(calculate): ...`).
- [x] I have updated `README.md` if I added a new theme or URL
parameter.
- [x] I have started the repo.
- [x] I have made sure that i have only one commit to merge in this PR.
- [x] The SVG output matches the CommitPulse "premium quality" aesthetic
standard (no raw elements, smooth animations, correct fonts).
- [x] (Recommended) I joined the CommitPulse Discord community for
contributor discussions, mentorship, and faster PR support.

Author: JhaSourav07

services/github/refresh-rate-limiter.test.ts

@@ -0,0 +1,78 @@
+import { beforeEach, describe, expect, it, vi } from 'vitest';
+import { refreshRateLimiter } from './refresh-rate-limiter';
+
+describe('RefreshRateLimiter', () => {
+  beforeEach(() => {
+    refreshRateLimiter.reset();
+    delete process.env.MAX_REFRESHES_PER_HOUR;
+    vi.restoreAllMocks();
+  });
+
+  it('allows the initial refresh request from an IP', () => {
+    const result = refreshRateLimiter.checkLimit('127.0.0.1');
+
+    expect(result.success).toBe(true);
+    expect(result.limit).toBe(3);
+    expect(result.remaining).toBe(2);
+  });
+
+  it('blocks requests after the limit is reached within the same window', () => {
+    refreshRateLimiter.setLimit(3);
+
+    refreshRateLimiter.checkLimit('127.0.0.1');
+    refreshRateLimiter.checkLimit('127.0.0.1');
+    refreshRateLimiter.checkLimit('127.0.0.1');
+
+    const blocked = refreshRateLimiter.checkLimit('127.0.0.1');
+
+    expect(blocked.success).toBe(false);
+    expect(blocked.remaining).toBe(0);
+    expect(blocked.limit).toBe(3);
+  });
+
+  it('resets the limit after the cooldown window expires', () => {
+    vi.useFakeTimers();
+
+    refreshRateLimiter.setLimit(2, 1000);
+
+    refreshRateLimiter.checkLimit('127.0.0.1');
+    refreshRateLimiter.checkLimit('127.0.0.1');
+
+    expect(refreshRateLimiter.checkLimit('127.0.0.1').success).toBe(false);
+
+    vi.advanceTimersByTime(1001);
+
+    const result = refreshRateLimiter.checkLimit('127.0.0.1');
+
+    expect(result.success).toBe(true);
+    expect(result.remaining).toBe(1);
+
+    vi.useRealTimers();
+  });
+
+  it('returns correct reset timestamp information', () => {
+    vi.useFakeTimers();
+
+    const now = new Date('2025-01-01T00:00:00Z');
+    vi.setSystemTime(now);
+
+    refreshRateLimiter.setLimit(3, 60_000);
+
+    const result = refreshRateLimiter.checkLimit('127.0.0.1');
+
+    expect(result.reset).toBe(now.getTime() + 60_000);
+
+    vi.useRealTimers();
+  });
+
+  it('uses MAX_REFRESHES_PER_HOUR environment override', () => {
+    process.env.MAX_REFRESHES_PER_HOUR = '5';
+
+    refreshRateLimiter.reset();
+
+    const result = refreshRateLimiter.checkLimit('127.0.0.1');
+
+    expect(result.limit).toBe(5);
+    expect(result.remaining).toBe(4);
+  });
+});