refactor(command): update parsing to use registry-based system

Update the command parsing layer to use the new CmdRegistry:

- parse_line() now uses default_registry() and returns Vec<Box<dyn Cmd>>
- parse_line_with() accepts a registry parameter for custom registries
- Tokenization replaced direct Command construction with registry.parse()
- Updated tests to verify command names instead of struct fields
- Removed parse_command() and helper functions (require_args, parse_coords,
  etc.)

The parser now delegates command construction to the registry, which
allows commands to be defined and registered in one place.

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

src/command/mod.rs

@@ -1,16 +1,12 @@
 //! Command layer — all model mutations go through this layer so they can be
 //! replayed, scripted, and tested without the TUI.
 //!
-//! Each command is a JSON object: `{"op": "CommandName", ...args}`.
-//! The headless CLI (--cmd / --script) routes through here, and the TUI
-//! App also calls dispatch() for every user action that mutates state.
+//! Commands are trait objects (`dyn Cmd`) that produce effects (`dyn Effect`).
+//! The headless CLI (--cmd / --script) parses Forth-style text into effects
+//! and applies them directly.
 
 pub mod cmd;
-pub mod dispatch;
 pub mod keymap;
 pub mod parse;
-pub mod types;
 
-pub use dispatch::dispatch;
 pub use parse::parse_line;
-pub use types::{Command, CommandResult};