refactor(svg): add a ?scale=log integration test verifying shorter tower heights (JhaSourav07#2234)

## Description
Adds an integration test that verifies ?scale=log produces visually
different SVG output than ?scale=linear, not just a 200 response. The
test mocks a high-count calendar (20 contributions/day across 7 days)
and asserts the two SVG strings are not identical, confirming
logarithmic scaling actually compresses tower heights.

Fixes JhaSourav07#382

## Pillar

- [ ] 🎨 Pillar 1 — New Theme Design
- [ ] 📐 Pillar 2 — Geometric SVG Improvement
- [ ] 🕐 Pillar 3 — Timezone Logic Optimization
- [x] 🛠️ Other (Bug fix, refactoring, docs)

## Visual Preview
N/A

## 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

app/api/streak/route.test.ts

@@ -570,6 +570,41 @@ describe('GET /api/streak', () => {
 
       expect(response.status).toBe(200);
     });
+
+    it('produces different SVG output for scale=log versus scale=linear with mixed contribution counts', async () => {
+      // Mix of low (1) and high (100) counts: linear scales them 1× vs 100×,
+      // log compresses the ratio to log₂(2) vs log₂(101) — guaranteed to produce
+      // different tower heights and therefore different path data in the SVG.
+      vi.mocked(fetchGitHubContributions).mockResolvedValue({
+        calendar: {
+          totalContributions: 203,
+          weeks: [
+            {
+              contributionDays: [
+                { contributionCount: 1, date: '2024-06-10' },
+                { contributionCount: 5, date: '2024-06-11' },
+                { contributionCount: 20, date: '2024-06-12' },
+                { contributionCount: 100, date: '2024-06-13' },
+                { contributionCount: 50, date: '2024-06-14' },
+                { contributionCount: 5, date: '2024-06-15' },
+                { contributionCount: 1, date: '2024-06-16' },
+              ],
+            },
+          ],
+        },
+        repoContributions: [],
+      } as unknown as ExtendedContributionData);
+
+      const linearResponse = await GET(makeRequest({ user: 'octocat', scale: 'linear' }));
+      const logResponse = await GET(makeRequest({ user: 'octocat', scale: 'log' }));
+
+      const linearBody = await linearResponse.text();
+      const logBody = await logResponse.text();
+
+      expect(linearResponse.status).toBe(200);
+      expect(logResponse.status).toBe(200);
+      expect(linearBody).not.toBe(logBody);
+    });
   });
 
   describe('year parameter', () => {