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]>

pyproject.toml

@@ -32,16 +32,13 @@ classifiers = [
 dependencies = [
     "PyYAML>=6.0",
     "requests>=2.28",
+    "PySide6>=6.5",
 ]
 
 [project.optional-dependencies]
-tui = [
-    "urwid>=2.1.0",
-]
 dev = [
     "pytest>=7.0",
     "pytest-cov>=4.0",
-    "urwid>=2.1.0",
 ]
 registry = [
     "Flask>=2.3",
@@ -50,7 +47,6 @@ registry = [
     "gunicorn>=21.0",
 ]
 all = [
-    "urwid>=2.1.0",
     "Flask>=2.3",
     "argon2-cffi>=21.0",
     "sentry-sdk[flask]>=1.0",