Convert TUI to PySide6 desktop GUI

Major UI overhaul replacing the urwid-based Terminal UI with a modern
PySide6 desktop application.

New GUI features:
- Sidebar navigation (My Tools, Registry, Providers)
- Tool Builder with visual form for creating/editing tools
- Registry browser with search and one-click install
- Provider management page
- Connect dialog for account pairing
- Publish dialog for sharing tools

- Keyboard shortcuts (Ctrl+N, Ctrl+S, Ctrl+R, Ctrl+1/2/3, Escape, Ctrl+Q)
- Window geometry persistence (remembers size/position)
- Modern clean stylesheet

Removed:
- ui.py, ui_snack.py, ui_registry.py, ui_urwid.py
- ui_urwid/ directory (urwid TUI implementation)

Updated:
- pyproject.toml: PySide6 now required, removed urwid
- CLI entry points to launch GUI
- All documentation (README, CLAUDE.md, AGENTS.md, wiki)

Co-Authored-By: Claude Opus 4.5 <[email protected]>

CLAUDE.md

@@ -21,21 +21,22 @@ pytest tests/test.py::test_name
 # Run the CLI
 python -m cmdforge.cli
 
-# Launch the UI
-cmdforge ui
+# Launch the GUI
+cmdforge
 ```
 
 ## Architecture
 
 ### Core Modules (`src/cmdforge/`)
 
-- **cli.py**: Entry point (`cmdforge` command). Routes subcommands: list, create, edit, delete, test, run, ui, refresh
+- **cli/**: CLI commands entry points (`cmdforge` command). Routes subcommands: list, create, edit, delete, test, run, refresh
 - **tool.py**: Tool definition dataclasses (`Tool`, `ToolArgument`, `PromptStep`, `CodeStep`), YAML config loading/saving, wrapper script generation
 - **runner.py**: Execution engine. Runs tool steps sequentially, handles variable substitution (`{input}`, `{varname}`), executes Python code steps via `exec()`
 - **providers.py**: Provider abstraction. Calls AI CLI tools via subprocess, reads provider configs from `~/.cmdforge/providers.yaml`
-- **ui.py**: UI dispatcher - selects between urwid and snack implementations
-- **ui_urwid.py**: Full TUI implementation using urwid library
-- **ui_snack.py**: Fallback TUI using python-newt/snack
+- **gui/**: PySide6 desktop GUI
+  - **main_window.py**: Main application window with sidebar navigation
+  - **pages/**: Tools page, Tool Builder, Registry browser, Providers management
+  - **dialogs/**: Step editors, Argument editor, Provider dialog, Connect/Publish dialogs
 
 ### Key Paths