Add organization compatibility with prefix detection (@org, org:, org/)

[Copilot]

This PR implements organization compatibility for GitLang, extending the application to support GitHub organizations in addition to users.

What's New

GitLang now supports three organization prefix formats:

• @netflix - Standard @ prefix
• org:microsoft - Colon-separated format
• org/google - Slash-separated format

Implementation Details

Server-side Changes

• Enhanced repositories.ts: Added organization detection logic that uses GitHub's listForOrg API for organizations vs listForUser API for users
• Smart API routing: Organizations use type: 'public' parameter while users continue using type: 'owner'
• Prefix parsing: Cleanly extracts organization names from prefixed input

Client-side Changes

• URL preservation: Maintains original input format in browser URLs (e.g., gitlang.net/@facebook)
• API compatibility: Strips prefixes when making GitHub API calls while preserving display format
• Seamless integration: Works with existing repo-specific queries (e.g., @facebook/react)

User Experience

• Updated placeholder: Changed from [ username / repo ] to [ username / repo ] or [ @org ]
• Enhanced descriptions: Updated app copy to reflect "username/organization" support
• Backward compatibility: All existing user workflows remain unchanged

Usage Examples

# Organization total language usage
gitlang.net/@netflix
gitlang.net/org:microsoft  
gitlang.net/org/google

# Organization repository-specific  
gitlang.net/@facebook/react
gitlang.net/org:microsoft/typescript

# Existing user functionality (unchanged)
gitlang.net/chiefmikey
gitlang.net/chiefmikey/gitlang

The language fetching logic requires no changes since GitHub's API uses the same owner/repo pattern for both users and organizations.

Fixes #90.

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