refactor(command): rename commands and extract panel/axis parsers

Rename several commands for consistency:
- save -> save-as (SaveAsCmd)
- save-cmd -> save (SaveCmd)
- enter-search -> search (EnterSearchMode)
- enter-edit -> enter-edit-mode (EnterEditMode)
- exit-search -> exit-search-mode (ExitSearchMode)

Add new commands:
- search-or-category-add
- search-append-char
- search-pop-char
- toggle-panel-and-focus
- toggle-panel-visibility
- command-mode-backspace

Extract parse_panel() and parse_axis() helper functions to replace
repeated match statements. Update documentation comments to reflect
quasi-lisp syntax instead of Forth-style.

Co-Authored-By: fiddlerwoaroof/git-smart-commit (unsloth/Qwen3.5-35B-A3B-GGUF:Q5_K_M)

src/command/parse.rs

@@ -1,4 +1,4 @@
-//! Forth-style prefix command parser.
+//! Quasi-lisp prefix command parser.
 //!
 //! Syntax: `word arg1 arg2 ...`
 //! Multiple commands on one line separated by `.`