Ergonomics and QoL improvements

## Overview
Quality of life improvements and ergonomic enhancements accumulated during recent development.

## Changes
- [ ] Consistent diffview keymaps for conflict (with same keymaps between diffview.lua and keymaps.lua)
- [x] Markdown preview keymaps for checkmate.nvim
- [x] Keymap refinements for better ergonomics
- [x] Test utilities reorganization and cleanup
- [x] Firefox history keymap

## Files Modified
- `lua/plugins/diffview.lua` - Git diff workflow improvements
- `lua/plugins/file-history.lua` - File history enhancements
- `lua/plugins/markdown-preview.lua` - Preview optimizations
- `lua/config/keymaps.lua` - Ergonomic keymap adjustments
- `lua/config/tests/test_keymaps_conflicts.lua` - New conflict detection utility
- `lazy-lock.json` - Dependency updates

## Focus Areas
- Better git workflow integration
- Improved markdown editing experience
- Enhanced keymap ergonomics
- Better testing utilities

## Branch
`feature/implement-multicursor`