feat(ui): move game folder picker into settings

The design update moved game-folder configuration out of launcher chrome and
into Settings > Library. Follow that contract in the runtime UI without
changing the existing storage or Tauri directory commands.

The top bar now leaves its right edge for the kebab menu. Settings owns a new
Game folder row that shows a valid selected path with a neutral Change button,
or the red Not set state with a stronger Choose button when no accessible
directory is configured. Both the empty-library state and the Settings row
still use the existing native directory picker, so existing saved paths and
rescans keep their current behavior.

Keep useGameDirectory as the directory-state owner and expose the shared
hasGameDirectory boolean from that hook so the grid and Settings field agree on
what counts as configured.

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

Refs: 62b409f4bfc4995c25461776107d28f52b24f30e

crates/lanspread-tauri-deno-ts/src/styles/launcher.css

@@ -394,44 +394,6 @@
   color: var(--accent);
 }
 
-/* Game-folder button: icon + short label.
-   Full path lives in tooltip + aria-label, not on-screen. */
-.dirbtn {
-  position: relative;
-  display: inline-flex;
-  align-items: center;
-  gap: 8px;
-  height: 36px;
-  padding: 0 14px 0 12px;
-  background: var(--bg-2);
-  border: 1px solid var(--bd-1);
-  border-radius: 8px;
-  color: var(--t-1);
-  font: inherit;
-  font-size: 12.5px;
-  font-weight: 600;
-  cursor: pointer;
-  white-space: nowrap;
-  flex-shrink: 0;
-  transition:
-    border-color 0.15s,
-    color 0.15s,
-    background 0.15s;
-}
-.dirbtn:hover {
-  border-color: var(--bd-2);
-}
-.dirbtn-label {
-  line-height: 1;
-}
-.dirbtn-unset {
-  border-color: color-mix(in srgb, var(--danger) 35%, var(--bd-1));
-}
-.dirbtn-unset:hover {
-  border-color: color-mix(in srgb, var(--danger) 55%, var(--bd-2));
-  background: color-mix(in srgb, var(--danger) 8%, var(--bg-2));
-}
-
 /* Kebab menu */
 .kebab {
   position: relative;
@@ -1600,6 +1562,86 @@
   font-weight: 500;
 }
 
+/* Settings: game-folder field */
+.folder-field {
+  display: inline-flex;
+  align-items: center;
+  gap: 8px;
+  width: 340px;
+  height: 36px;
+  padding: 0 4px 0 12px;
+  background: var(--bg-3);
+  border: 1px solid var(--bd-1);
+  border-radius: 8px;
+  transition:
+    border-color 0.15s,
+    background 0.15s;
+}
+.folder-field:hover {
+  border-color: var(--bd-2);
+}
+.folder-field.is-unset {
+  border-color: color-mix(in srgb, var(--danger) 35%, var(--bd-1));
+  background: color-mix(in srgb, var(--danger) 6%, var(--bg-3));
+}
+.folder-field.is-unset:hover {
+  border-color: color-mix(in srgb, var(--danger) 55%, var(--bd-2));
+}
+.folder-field-icon {
+  color: var(--t-3);
+  flex-shrink: 0;
+}
+.folder-field.is-unset .folder-field-icon {
+  color: #f87171;
+}
+.folder-field-path {
+  flex: 1;
+  min-width: 0;
+  font-family: ui-monospace, "SF Mono", Menlo, Consolas, monospace;
+  font-size: 12px;
+  color: var(--t-1);
+  white-space: nowrap;
+  overflow: hidden;
+  text-overflow: ellipsis;
+  direction: rtl;
+  text-align: left;
+  unicode-bidi: plaintext;
+}
+.folder-field-empty {
+  font-family: var(--font-ui);
+  font-size: 12.5px;
+  font-weight: 600;
+  color: #f87171;
+  letter-spacing: 0;
+}
+.folder-field-btn {
+  flex-shrink: 0;
+  height: 28px;
+  padding: 0 12px;
+  border: 0;
+  border-radius: 6px;
+  background: rgba(255, 255, 255, 0.06);
+  color: var(--t-1);
+  font: inherit;
+  font-size: 12.5px;
+  font-weight: 600;
+  letter-spacing: 0;
+  cursor: pointer;
+  transition:
+    background 0.15s,
+    color 0.15s;
+}
+.folder-field-btn:hover {
+  background: rgba(255, 255, 255, 0.12);
+}
+.folder-field.is-unset .folder-field-btn {
+  background: color-mix(in srgb, var(--accent) 85%, transparent);
+  color: #fff;
+}
+.folder-field.is-unset .folder-field-btn:hover {
+  background: var(--accent);
+}
+
 /* Settings: color swatches */
 .swatch-row {
   display: inline-flex;