feat(panel): island, rail by day, companion mode beside a deep note, cached index and threads, obsidian skin for strips

tests/smoke.mjs

@@ -226,10 +226,8 @@ flushSync();
 await settle();
 const rows = [...dom.window.document.querySelectorAll("[data-row]")];
 check(
-  "switcher lists open conversations grouped",
-  rows.length >= 4 &&
-    text().includes("Branches") &&
-    text().includes("Deep chats"),
+  "switcher lists open conversations grouped by day",
+  rows.length >= 4 && text().includes("Today"),
   `${rows.length}`
 );
 check(