feat: Add lualine integration and enhanced per-buffer IM management

[itshare4u]

🚀 New Features

This PR adds comprehensive lualine integration and enhanced per-buffer input method management.

✨ 1. Lualine Component Integration

A new lualine component that shows which input method will be used when entering insert mode:

• Always visible: Shows IM info even in normal mode
• Context-aware: Different display for each buffer/window
• No fallback assumptions: Only shows when context is actually known
• Customizable: Colors, icons, and display can be configured

Basic Usage:

require('lualine').setup {
    sections = {
        lualine_c = { 
            'filename',
            require('im_select.lualine').get_component()
        },
    }
}

Advanced Usage:

require('lualine').setup {
    sections = {
        lualine_x = { 
            require('im_select.lualine').get_component({
                color_english = { fg = "#98be65", gui = "bold" },
                color_other = { fg = "#ECBE7B", gui = "bold" },
                icon = "⌨️",
            })
        },
    }
}

🔧 2. Enhanced IM Context Management

Display Name Storage

• Automatically converts IM identifiers to readable display names (EN, VI, CN, JP, etc.)
• Stores both raw IM and display name for performance
• Single source of truth for display logic

Improved Per-Buffer Management

• Better priority: Buffer pinned > Buffer > Window
• Consistent storage: Both vim.b.im_select_context and vim.b.im_select_display_name
• Enhanced pin command: Shows both display name and raw IM identifier

📁 Files Added/Modified

New Files:

• lua/im_select/lualine.lua - Lualine component implementation
• examples/lualine_config.lua - Usage examples and configurations

Modified Files:

• lua/im_select.lua - Added display name logic and enhanced storage
• README.md - Comprehensive lualine integration documentation

🎯 Benefits

For Users:

• Preview IM: Know which language you'll type before entering insert mode
• Visual feedback: Clear indication in statusline with colors and icons
• Per-context awareness: Each buffer remembers its own input method
• No surprises: Only shows reliable information, no guessing

For Developers:

• Clean architecture: Separation between core logic and UI display
• Extensible: Easy to add new IM support or customize display
• Performance: Cached display names, no repeated conversions
• Maintainable: Single place to modify display logic

🧪 Testing

Tested extensively on macOS with:

• Vietnamese input method (com.apple.inputmethod.VietnameseIM.VietnameseSimpleTelex)
• Multiple buffers and windows
• Buffer pinning scenarios
• Lualine integration in various sections

📚 Usage Examples

Display shows context-aware IM:

• Buffer with Vietnamese context → ⌨️ VI
• Buffer with English context → ⌨️ EN
• New buffer with no context → (nothing displayed)
• Pinned buffer → Always shows pinned IM

🔄 Backward Compatibility

• All existing functionality preserved
• No breaking changes to existing configurations
• Lualine integration is completely optional
• Enhanced commands are additive only

💡 Implementation Highlights

1. Smart Context Detection: Uses same priority logic as core IM switching
2. Performance Optimized: Display names cached at source, lualine just reads
3. Cross-platform: Works with macOS, Windows, WSL, and Linux IM systems
4. User-friendly: Clear visual feedback without cluttering the interface

This enhancement makes im-select.nvim much more user-friendly for multilingual workflows while maintaining its reliability and performance.