feat: Add AI-Powered Automated Unit Test Suite Generator

[Rafiaminhaj]

Describe the changes

This PR implements the AI-Powered Automated Unit Test Suite Generator feature under GSSoC '26 (resolving #1091).

Backend Implementation

• Schemas: Added TestGenerationRequest, TestSummary, and TestGenerationResponse classes in backend/app/schemas.py.
• Services: Added generate_tests method in LLMAnalysisClient (backend/app/services/llm_analysis.py) to interface with LLM backend providers.
• Router: Created the API router in backend/app/routers/test_generator.py for language-specific framework auto-detection.
• App Main: Registered the router, enabled rate-limiting in Starlette middleware, and fixed Unicode start-log encoding crashes on Windows consoles.
• Tests: Added API endpoint tests in backend/tests/test_endpoints.py.

Frontend Implementation

• Controls Pane: Added "Test Gen" mode button and target test framework dropdown + mock calls checkbox in frontend/index.html.
• Results Tab/Pane: Added Test Gen results tab and content pane containing loading shimmers, summary cards, and clean test code viewers.
• UX Polish: Integrated framework auto-selection on programming language change, copy code with visual feedback micro-animations, and file exporter/download with matching extensions.
• Localization: Added translations for English, Tamil, Hindi, and French.

Related Issue

Closes #1091

Checklist

• My PR title follows the format: feat/fix/docs/test: short description
• I have added tests for new features
• Verify all 433 unit tests pass successfully

[imDarshanGK]

@Rafiaminhaj

[github-actions]

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