rename: the sign-in screen shows Inkwell's mark, and every tab says Inkwell

The login and register screens still drew a hard-coded "TS" tile. They now
use /icon.svg, the same mark the shell's header shows.

Browser tabs took index.html's static <title> and never changed it, so every
tab read the same, and some browsers showed the URL instead. usePageTitle,
mounted once in App.vue, sets "<page> · <site name>". Routes outside the shell
name themselves with meta.title. Board lenses use the lens name the header
already shows, now in useLensName so the tab and the header read from one
place.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

frontend/src/components/AppShell.vue

@@ -13,6 +13,7 @@ import Icon from "./Icon.vue";
 import ImportNotes from "./ImportNotes.vue";
 import LabelsModal from "./LabelsModal.vue";
 import { isDesktop } from "../desktop/bridge";
+import { useLensName } from "../composables/useLensName";
 import { facetsToQuery } from "../notes/facets";
 import { NOTE_SWATCH_CLASSES, resolveLabelColor } from "../notes/colors";
 
@@ -242,34 +243,7 @@ watch(
   },
 );
 
-/**
- * What to call the lens currently in view.
- *
- * Keyed off the route name rather than each view declaring its own title, so the
- * label sits in one place and can't go missing (the board never had one)
- * or drift in styling (timeline and reminders each had their own h1).
- *
- * A label lens is named by the label itself — "Groceries" is what the user came
- * looking for; "Label" would tell them nothing they didn't already know.
- */
-const lensName = computed<string>(() => {
-  switch (route.name) {
-    case "archive":
-      return "Archive";
-    case "trash":
-      return "Trash";
-    case "timeline":
-      return "Timeline";
-    case "reminders":
-      return "Reminders";
-    case "label":
-      // The store may not have loaded yet on a deep link; fall back rather than
-      // flashing an empty slot.
-      return labels.items.find((l) => l.id === String(route.params.id))?.name ?? "Label";
-    default:
-      return "Notes";
-  }
-});
+const lensName = useLensName();
 
 async function signOut() {
   await session.logout();