fix: rename _registry to _tool_registry to avoid shadowing Textual internal

The App base class uses _registry (WeakSet) for DOM node tracking.
Our _registry attribute for the tool registry was shadowing it with None,
causing a TypeError during shutdown.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

app/ui/app.py

@@ -47,7 +47,7 @@ class SneakyCodeApp(App):
         self._ctx: SessionContext | None = None
         self._agent: AgentLoop | None = None
         self._client: LLMClient | None = None
-        self._registry = None
+        self._tool_registry = None
         self._permissions: PermissionsService | None = None
         self._current_worker: Worker | None = None
         self._cancel_count = 0
@@ -69,7 +69,7 @@ class SneakyCodeApp(App):
         # Create long-lived agent dependencies (reused across turns)
         self._client = LLMClient(self._config.llm)
         await self._client.__aenter__()
-        self._registry = create_default_registry(self._config.agent.workspace_root, self._config)
+        self._tool_registry = create_default_registry(self._config.agent.workspace_root, self._config)
         self._permissions = PermissionsService(self._config.permissions)
 
         # Set up permission prompt callback
@@ -178,7 +178,7 @@ class SneakyCodeApp(App):
 
         agent = AgentLoop(
             self._config, self._ctx, self._client, handler,
-            self._registry, self._permissions, display,
+            self._tool_registry, self._permissions, display,
         )
 
         await agent.run_turn(user_input)