feat: add Antigravity as an "Open in editor" target (#1424)

Registers the Google Antigravity IDE so the workspace Open-in-editor
picker detects and launches it (PATH probe for the "antigravity"
command), alongside Cursor, VS Code, WebStorm, and Zed.

- desktop: add the target to BUILT_IN_EDITOR_TARGETS (kind: editor).
- app: add "antigravity" to the known editor-target id set and map its
  bundled icon.

Co-authored-by: Mathias Kurz <mkurz@stamus-networks.com>

packages/desktop/src/features/editor-targets.ts

@@ -73,6 +73,7 @@ const BUILT_IN_EDITOR_TARGETS: readonly EditorTargetDefinition[] = [
   { id: "vscode", label: "VS Code", kind: "editor", command: "code" },
   { id: "webstorm", label: "WebStorm", kind: "editor", command: "webstorm" },
   { id: "zed", label: "Zed", kind: "editor", command: "zed" },
+  { id: "antigravity", label: "Antigravity", kind: "editor", command: "antigravity" },
   {
     id: "finder",
     label: "Finder",