feat: Add 250-character limit validation for username input with comprehensive feedback

[Copilot]

Problem

Users could enter or share links with excessively long username lists that could cause performance issues and API rate limiting. The application lacked validation to prevent username combinations exceeding reasonable character limits.

Solution

This PR implements a comprehensive 250-character limit validation system that works across all username input scenarios:

✅ Manual Entry Validation

When users manually type usernames that exceed 250 characters total, they receive immediate feedback:

Username list is too long (312 characters). Please limit the combined usernames to 250 characters.

✅ URL Restoration Validation

When users access shared links with excessive username parameters, validation errors are displayed and search operations are prevented:

// Example URL that would trigger validation
/git-vegas/?username=verylongusername1,verylongusername2,verylongusername3...

✅ Search Operation Protection

The validation is integrated into the core search flow, ensuring that:

• validateSearchParams() checks username character limits before API calls
• validateUsernameList() provides accurate character counts in error messages
• URL parameter processing shows validation errors for shared links

Technical Implementation

Core Validation (src/utils.ts)

• Enhanced validateUsernameList() to count total character length of all usernames
• Provides precise character count feedback (e.g., "252 characters" when limit exceeded)

Search Integration (src/utils/githubSearch.ts)

• Updated validateSearchParams() to use username validation
• Ensures character limits are enforced before expensive API operations

URL Handling (src/hooks/useGitHubFormState.ts)

• Enhanced URL parameter processing to display validation errors
• Users see clear feedback when accessing invalid shared links

Testing

Added comprehensive test coverage including:

• Exact 250-character boundary testing (valid case)
• 251+ character testing (invalid cases)
• URL restoration scenarios with both valid and invalid character limits
• Integration tests ensuring validation works across all entry points

User Experience

• Clear feedback: Users see exactly how many characters they've used
• Prevention: Invalid operations are blocked before API calls
• Consistency: Same validation applies to manual entry and URL restoration
• Accessibility: Error messages are descriptive and actionable

This ensures better performance, prevents API abuse, and provides a consistent user experience across all username input methods.

Warning

Firewall rules blocked me from connecting to one or more addresses

I tried to connect to the following addresses, but was blocked by firewall rules:

• https://api.github.com/users/urluser
  • Triggering command: node (vitest 1) (http block)

If you need me to access, download, or install something from one of these locations, you can either:

• Configure Actions setup steps to set up my environment, which run before the firewall is enabled
• Add the appropriate URLs or hosts to the custom allowlist in this repository's Copilot coding agent settings (admins only)

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