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]>

src/cmdforge/cli/registry_commands.py

@@ -501,14 +501,7 @@ def _cmd_registry_my_tools(args):
 
 
 def _cmd_registry_browse(args):
-    """Browse tools (TUI)."""
-    try:
-        from ..ui_registry import run_registry_browser
-        return run_registry_browser()
-    except ImportError:
-        print("TUI browser requires urwid. Install with:", file=sys.stderr)
-        print("  pip install 'cmdforge[tui]'", file=sys.stderr)
-        print()
-        print("Or search from command line:", file=sys.stderr)
-        print("  cmdforge registry search <query>", file=sys.stderr)
-        return 1
+    """Browse tools (GUI)."""
+    from ..gui import run_gui
+    # Launch GUI - it will open to Registry page
+    return run_gui()

src/cmdforge/cli/tool_commands.py

@@ -7,7 +7,7 @@ from ..tool import (
     list_tools, load_tool, save_tool, delete_tool, get_tools_dir,
     Tool, ToolArgument, PromptStep, CodeStep, ToolStep
 )
-from ..ui import run_ui
+from ..gui import run_gui
 
 
 def cmd_list(args):
@@ -248,9 +248,8 @@ def cmd_run(args):
 
 
 def cmd_ui(args):
-    """Launch the interactive UI."""
-    run_ui()
-    return 0
+    """Launch the interactive GUI."""
+    return run_gui()
 
 
 def cmd_refresh(args):