feat: add Treesitter support and fixed-size UI (#15)

Implement comprehensive Treesitter integration for more accurate context detection when generating mark names, with fallback to regex patterns.
Redesign the UI with a fixed 80x20 window size, featuring dimmed help text at the bottom and visual separators between sections.

Author: alexekdahl

README.md

@@ -18,7 +18,7 @@ Vim's built-in marks are great, but they're global and get messy fast. Marksman
 
 - **Project-scoped marks** - Each project gets its own isolated set of bookmarks
 - **Persistent storage** - Your marks survive Neovim restarts with automatic backup
-- **Smart naming** - Context-aware auto-generation based on code structure
+- **Smart naming** - Context-aware auto-generation using Treesitter and pattern matching
 - **Quick access** - Jump to marks with single keys or interactive UI
 - **Enhanced search** - Find marks by name, file path, or content with real-time filtering
 - **Mark reordering** - Move marks up/down to organize them as needed