fix(profiles): keep the picker chrome-free

/profiles was unknown to the layout shell, so reaching it from Settings
rendered the bottom nav and global header over the picker -- letting
someone tab straight past the profile they were being asked to choose,
and offering an in-app mini player as a route back into the previous
profile's queue.

Grouped with /login throughout layoutShell: it is a gate, not a page. OS
lockscreen transport controls are unaffected, which is what keeps playing
audio controllable while the app is locked.

src/lib/utils/layoutShell.ts

@@ -28,10 +28,19 @@ export interface BottomUiVisibilityInput {
 
 /**
  * The bottom nav is shown on every authenticated route except the full-screen
- * player and the login route.
+ * player, the login route, and the profile picker.
+ *
+ * `/profiles` is grouped with `/login` throughout this module because it is a
+ * gate rather than a page: a nav bar over "who's watching" lets someone tab
+ * straight past the choice they were being asked to make.
  */
 export function showBottomNav({ pathname, isAuthenticated }: BottomUiVisibilityInput): boolean {
-  return isAuthenticated && !pathname.startsWith("/player/") && !pathname.startsWith("/login");
+  return (
+    isAuthenticated &&
+    !pathname.startsWith("/player/") &&
+    !pathname.startsWith("/login") &&
+    !pathname.startsWith("/profiles")
+  );
 }
 
 /**
@@ -44,6 +53,7 @@ export function showGlobalMiniPlayer({ pathname }: { pathname: string }): boolea
   return (
     !pathname.startsWith("/player/") &&
     !pathname.startsWith("/login") &&
+    !pathname.startsWith("/profiles") &&
     !pathname.startsWith("/settings")
   );
 }
@@ -58,7 +68,8 @@ export function routeOwnsLayout({ pathname }: { pathname: string }): boolean {
   return (
     pathname.startsWith("/library") ||
     pathname.startsWith("/player/") ||
-    pathname.startsWith("/login")
+    pathname.startsWith("/login") ||
+    pathname.startsWith("/profiles")
   );
 }
 
@@ -69,7 +80,7 @@ export function routeOwnsLayout({ pathname }: { pathname: string }): boolean {
  * Routes that own their layout (library) render their own AppHeader, so the
  * root must not double it up. `/settings` owns its content but deliberately has
  * no account menu (the user is already there). `/player/*` and `/login` are
- * immersive/chrome-free. Everything else authenticated (`/`, `/search`,
+ * immersive/chrome-free, as is `/profiles`. Everything else authenticated (`/`, `/search`,
  * `/downloads`) gets the header from the root — the whole point of UR-054.
  *
  * TRACES: UR-054 | DR-076
@@ -109,7 +120,8 @@ export function showBottomUi(input: BottomUiVisibilityInput): boolean {
  * Exactly one element may reserve it. BottomUi owns it whenever it renders,
  * because the padding belongs *inside* its surface box so the colour extends
  * behind the bar rather than leaving a strip of page background. On routes with
- * no bottom UI at all (login, the full-screen player) nothing else would, so
+ * no bottom UI at all (login, the profile picker, the full-screen player)
+ * nothing else would, so
  * the shell takes it.
  *
  * TRACES: UR-066 | DR-112