feat(format): add dot-repeat support for normal mode formatting actions

[YousefHadder]

Description

Implements dot-repeat support for normal mode formatting actions, allowing users to quickly apply the same formatting to multiple words using Vim's native . command.

Closes #131

Changes

Implementation

• Added operatorfunc-based dot-repeat for normal mode formatting commands
• Uses native Neovim g@l operator mechanism (no external dependencies)
• Optional integration with repeat.vim if available
• Visual mode formatting works normally (no dot-repeat by design)

Files Modified

• lua/markdown-plus/format/init.lua - Core implementation with operatorfunc callbacks
• lua/markdown-plus/keymap_helper.lua - Added expr mapping support
• README.md - Added feature documentation with examples
• doc/markdown-plus.txt - Updated help docs with usage guide

Usage Example

word1 word2 word3

1. Position cursor on "word1"
2. Press <leader>mb  →  **word1** word2 word3
3. Move cursor to "word2"
4. Press .  →  **word1** **word2** word3
5. Move to "word3", press .  →  **word1** **word2** **word3**

Supported Commands

All normal mode formatting actions are now dot-repeatable:

• <leader>mb - Toggle bold
• <leader>mi - Toggle italic
• <leader>mc - Toggle inline code
• <leader>ms - Toggle strikethrough
• <leader>mC - Clear all formatting

Testing

• ✅ All 94 existing tests pass
• ✅ 0 linting errors
• ✅ Code properly formatted
• ✅ No breaking changes
• ✅ No new configuration required

Technical Details

The implementation uses Neovim's operatorfunc mechanism:

1. Normal mode mappings use expr = true and return "g@l"
2. Format type is stored in internal state
3. Operatorfunc callback applies the formatting
4. Native . command repeats the operator

This works without any external plugins, though it remains compatible with repeat.vim for enhanced functionality.

Documentation

All documentation has been updated:

• Feature description in README with concrete example
• Detailed usage guide in vimdoc
• Clear indication that visual mode doesn't support dot-repeat (by design)

[Copilot]

Pull Request Overview

This PR implements dot-repeat support for normal mode formatting actions in markdown-plus.nvim, enabling users to quickly apply the same formatting to multiple words using Vim's native . command. The implementation uses Neovim's operatorfunc mechanism without requiring external dependencies.

Key Changes:

• Added operatorfunc-based dot-repeat mechanism for formatting commands (bold, italic, strikethrough, code, clear formatting)
• Extended keymap helper to support expression mappings with per-mode configuration
• Updated documentation in README and vimdoc with usage examples

Reviewed Changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 7 comments.

File	Description
lua/markdown-plus/format/init.lua	Implements dot-repeat functionality via operatorfunc callbacks and wrapper functions
lua/markdown-plus/keymap_helper.lua	Adds support for expression mappings with per-mode expr flag
doc/markdown-plus.txt	Documents dot-repeat feature with usage examples
README.md	Adds dot-repeat feature description to feature list