On macOS, OpenIDEA is now listed under Finder's Open With for text and source files and for folders. It never becomes the default app for any of them: all document types are declared with rank Alternate, and only in tauri.macos.conf.json, so Windows and Linux installers register nothing.
Files opened from Finder, the Dock or a second instance share one routing path (plan_open). A file inside a local project that is already open, or still opening, goes to that project's window, choosing the deepest root when projects are nested. Any other file goes to the existing single-file window, or to a new one. A folder focuses the window that already has it open, otherwise it opens as a project. Paths that arrive before setup are queued and opened with the first launch.
The single-file window now closes with its last tab, restores its files the next time it opens, and only offers Open File and drop hints when empty. Also fixes a regression: reopening projects on startup no longer replaces a file opened at cold start.
Refs #128
