fix: rename middleware.ts to proxy.ts (Next.js 16.2.7 deprecation)

[Kokila-chandrakar]

Description

Fixes #4839

Next.js 16.2.7 deprecated the middleware.ts file convention in favor of proxy.ts.
This caused:

• Build warning: ⚠ The middleware file convention is deprecated. Please use proxy instead.
• CI failure: proxy.accessibility.test.ts imports from ./proxy which didn't exist, causing TS2307: Cannot find module './proxy'

Fix: Renamed middleware.ts → proxy.ts in the project root.

Pillar

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

Checklist before requesting a review:

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

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[github-actions]

🚨 Hey @Kokila-chandrakar, the CI Pipeline is failing on this PR and it has been marked as status:blocked.

Please fix the issues before this can be reviewed. Here's how:

1. Run checks locally before pushing:

npm run format:check   # Check Prettier formatting
npm run lint           # Run ESLint
npm run typecheck      # TypeScript type check
npm run test           # Run unit tests (Vitest)
npm run build          # Verify production build passes

2. Auto-fix common issues:

npm run format         # Auto-fix formatting with Prettier
npm run lint -- --fix  # Auto-fix lint errors where possible

3. Check the full failure log here:
👉 View CI Run

Once you push a fix and the CI passes, the status:blocked label will be removed automatically. 💪

[Kokila-chandrakar]

Hi @JhaSourav07 , @Aamod007
These test failures are pre-existing in the main branch and are unrelated to this PR.
This PR only renames middleware.ts to proxy.ts as required by Next.js 16.2.7.