test: added test cases for constants, points and telugukeyboard

Description:

Added comprehensive unit test coverage for core utility modules to improve reliability and ensure correct functionality.

• constants.test.ts (13 tests): Verified BACKEND_URL constant behavior including environment variable mapping (VITE_API_SERVER_URL), type validation, immutability, module exports, and URL edge cases (trailing slashes, ports, API paths).

• points.test.ts (40 tests): Tested API functions for user points and leaderboard:

  • getPointsToday()
  • getPointsStats()
  • getStreakStatus()
  • getGlobalLeaderboard() Covered success responses, error handling, empty data scenarios, and type validation using mocked API calls.

• teluguKeyboard.test.ts (145 tests): Extensive testing of Telugu transliteration engine:

  • Initialization and transliteration logic
  • Vowels, consonants, compound characters, and combinations
  • Multi-syllable words and edge cases
  • Suggestions, vowel combinations, base consonant extraction Achieved high coverage (~91.63% statements, 100% functions)

These tests significantly improve confidence in shared logic used across the application.

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Type of Change:

• Bug Fix
• Feature Development
• Documentation

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Testing:

• Tested on desktop
• Tested on mobile
• Tested in different browsers

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Screenshots (if applicable):

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Checklist:

• Code follows project style guidelines
• Self-review completed
• No console errors
• TypeScript types are correct

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closes #264 (closed)