refactor: remove bundled Claude Code binary support

- Remove all bundled/sidecar binary functionality
- Delete build scripts for fetching and building Claude executables
- Simplify binary detection to only support system installations
- Update UI to remove bundled installation options
- Update build configuration and documentation

src-tauri/tauri.conf.json

@@ -47,19 +47,5 @@
     "shell": {
       "open": true
     }
-  },
-  "bundle": {
-    "active": true,
-    "targets": "all",
-    "icon": [
-      "icons/32x32.png",
-      "icons/128x128.png",
-      "icons/128x128@2x.png",
-      "icons/icon.icns",
-      "icons/icon.png"
-    ],
-    "externalBin": [
-      "binaries/claude-code"
-    ]
   }
 }