feat(ui): label streamed installs as not shareable

NEXT_STEPS item 7 needed the installed-but-not-downloaded state to be
clear to users. Keep streamed installs in the installed visual state so
sorting, filters, and the primary Play action stay unchanged, but make the
sharing limitation visible in the UI.

Cards now label that state as `Not shareable`, while the detail modal
status says `Installed, not shareable`. Downloaded-and-installed games
keep the normal `Installed` wording.

Test Plan:
- just frontend-test
- just build
- git diff --check
- git diff --cached --check

Refs: NEXT_STEPS.md item 7

NEXT_STEPS.md

@@ -54,11 +54,12 @@ product-ready.
    The peer-cli harness now exposes `cancel-download` so cancellation scenarios
    exercise the same runtime path as the GUI.
 
-7. **Clean product semantics**
+7. **Done — Clean product semantics**
 
-   Decide how the UI labels this state. It is installed but not downloaded, so
-   “Local only” is technically correct, but users may need a clear affordance
-   like “Installed, not shareable”.
+   The UI now keeps streamed installs in the installed visual state while making
+   the sharing limitation explicit: cards show `Not shareable`, and the detail
+   modal status shows `Installed, not shareable`. Downloaded-and-installed games
+   keep the normal `Installed` label.
 
 My recommended next slice: make the provider abstraction final-ish, then
 implement a real one-pass provider. Everything else builds cleanly on that.