feat: Add git-scope issue command to open GitHub issues page

[ZaidQtaish]

Description

Implements the feature requested in #5 - adds a git-scope issue command that opens the GitHub issues page in the user's default browser.

Closes #5

Changes

• Added new git-scope issue command to open https://github.com/Bharath-code/git-scope/issues
• Create /internal/browser package for cross-platform browser launching
• Refactor TUI's openBrowserCmd() to use the shared browser package
• Update help text to document the new command

Fixes #

Type of Change

• 🐛 Bug fix (non-breaking change that fixes an issue)
• ✨ New feature (non-breaking change that adds functionality)
• 💥 Breaking change (fix or feature that would cause existing functionality to change)
• 📚 Documentation update
• 🔧 Refactoring (no functional changes)

Checklist

• I have tested my changes locally
• I have updated the documentation (if applicable)
• My code follows the project's style guidelines
• I have added tests that prove my fix/feature works (if applicable)

[Bharath-code]

its already duplicate of PR-7