feat: enable Computer Use with Python bridge replacing private native modules

Bypass all three gating layers (compile-time feature flag, subscription
check, GrowthBook remote config) and replace Anthropic's private native
modules (@ant/computer-use-swift, @ant/computer-use-input) with a Python
bridge using pyautogui + mss + pyobjc. Works on any macOS with any
Anthropic-protocol compatible model.

.gitignore

@@ -2,3 +2,7 @@
 .env.*
 !.env.example
 node_modules
+
+# Computer Use runtime (auto-generated)
+.runtime/
+extracted-natives/