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

crates/lanspread-tauri-deno-ts/src/lib/gameState.ts

@@ -82,6 +82,35 @@ export const deriveState = (game: Game): DerivedState => {
     return 'none';
 };
 
+export const isInstalledNotShareable = (game: Game): boolean =>
+    game.installed && !game.downloaded;
+
+export const stateChipLabel = (game: Game): string => {
+    const state = deriveState(game);
+    if (state === 'installed' && isInstalledNotShareable(game)) return 'Not shareable';
+    switch (state) {
+        case 'installed': return 'Installed';
+        case 'local': return 'Local';
+        case 'downloading': return 'Downloading';
+        case 'busy': return 'Working';
+        case 'none': return '';
+    }
+};
+
+export const gameStatusLabel = (game: Game): string => {
+    const state = deriveState(game);
+    if (state === 'installed' && isInstalledNotShareable(game)) {
+        return 'Installed, not shareable';
+    }
+    switch (state) {
+        case 'installed': return 'Installed';
+        case 'local': return 'Downloaded';
+        case 'downloading': return 'Downloading';
+        case 'busy': return 'Working…';
+        case 'none': return 'Not downloaded';
+    }
+};
+
 export const isUnavailable = (game: Game): boolean =>
     !game.installed
     && !game.downloaded