fix: handle Supabase admin client absence in wakatime API route(closes #2233)

[shauryavardhan1307]

Title

fix: handle Supabase admin client absence in wakatime API route

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PR Body

## Summary

Safely guards the `/api/wakatime` route against unconfigured Supabase admin credentials by checking `isSupabaseAdminAvailable` and returning a clean fallback instead of throwing unhandled 500 errors. This prevents CI/Playwright test suites and local development setups without Supabase from failing.

Closes #2233 
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## Type of Change

- [x] 🐛 Bug fix (non-breaking change that fixes an issue)
- [ ] ✨ New feature (non-breaking change that adds functionality)
- [ ] 💥 Breaking change (fix or feature that changes existing behavior)
- [ ] 📝 Documentation update
- [ ] ♻️ Refactor / code cleanup (no functional change)
- [ ] ⚡ Performance improvement
- [ ] 🔒 Security fix
- [ ] 🧪 Tests only

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## What Changed

- **[`src/lib/supabase.ts`](file:///d:/devtrack/src/lib/supabase.ts)**: Defined and exported `isSupabaseAdminAvailable` helper to check if credentials are set.
- **[`src/app/api/wakatime/route.ts`](file:///d:/devtrack/src/app/api/wakatime/route.ts)**: Imported `isSupabaseAdminAvailable` and added a defensive guard at the start of the `GET` handler to return a clean fallback `{ hasData: false, not_configured: true }` when credentials are absent.
- **[`test/wakatime-api.test.ts`](file:///d:/devtrack/test/wakatime-api.test.ts)**: Created a new unit test suite checking authenticated, unauthenticated, and unconfigured Supabase paths.

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## How to Test

1. Ensure Supabase credentials (`NEXT_PUBLIC_SUPABASE_URL`, `SUPABASE_SERVICE_ROLE_KEY`) are removed or set to placeholder values in your local `.env`.
2. Make a `GET` request to `/api/wakatime` (while authenticated).
3. Verify it returns `{ "hasData": false, "not_configured": true }` with a `200 OK` status rather than throwing a 500 error.
4. Run the unit tests to confirm they pass:
   ```bash
   npx vitest run test/wakatime-api.test.ts

Expected result:
The endpoint successfully falls back to a 200 response indicating Supabase is not configured instead of throwing a database connection crash.

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Screenshots / Recordings

N/A

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Checklist

• Linked the related issue above
• Self-reviewed my own diff
• No unnecessary console.log, debug code, or commented-out blocks
• npm run lint passes locally
• No TypeScript errors (npm run type-check)
• Added or updated tests where applicable
• Updated documentation / comments if behavior changed

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Accessibility (UI changes only)

Skip section (no UI impact).

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Additional Context

None.

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GSSoC Label Checklist 🏷️

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[shauryavardhan1307]

⚠️ Note on E2E / Visual Regression CI Failures

The failing E2E and Visual Regression checks are pre-existing issues on upstream/main and are completely unrelated to the changes in this PR:

1. [Dashboard E2E] no uncaught console errors on dashboard load:

   • Root Cause: React throws a duplicate key console warning in src/components/ContributionHeatmap.tsx. Around line 454, the legend elements are mapped using key={count}:

     [
       0,
       Math.ceil(maxCommits * 0.25),
       Math.ceil(maxCommits * 0.5),
       Math.ceil(maxCommits * 0.75),
       maxCommits,
     ].map((count) => ... key={count})

     When maxCommits is small (e.g., 1), the array evaluates to [0, 1, 1, 1, 1], which produces duplicate React keys (key={1}) and triggers a console warning that fails the console-error assertion.
   • Relation: Unrelated to our PR (this PR only modifies /api/wakatime and src/lib/supabase.ts).

2. settings page saves and reflects changes:

   • Root Cause: Playwright times out trying to toggle and assert the state of the sr-only checkbox (locator.check: Clicking the checkbox did not change its state). This is an interaction flakiness with hidden input overlays in the E2E spec.
   • Relation: Unrelated to our PR.

3. [Streak E2E] streak widget shows the mocked longest streak value:

   • Root Cause: The locator in e2e/streak.spec.ts fails to find the mocked streak value 21 due to recent upstream markup/layout refactorings.
   • Relation: Unrelated to our PR.

[Priyanshu-byte-coder]

The isSupabaseAdminAvailable guard already exists in this route. The only production code change is adding an explicit { status: 200 } which is already the default for NextResponse.json(). Please verify the fix addresses an actual issue not already handled.

[shauryavardhan1307]

My apologies! I opened the issue and branch before PR #1982 was merged into upstream/main. Since the isSupabaseAdminAvailable guard has already been added upstream and handles the fallback cleanly, this PR is indeed redundant.

I will close this PR and the associated issue now. Thank you for pointing that out!