profiler: switch Profiles / Card snapshots with tabs instead of two columns

The list view now has a centered pill row (Profiles | Card snapshots) and
shows one list at a time; the last active tab persists while the app is
open. Snapshot flows (scan, import) switch to the snapshots tab, profile
import switches to profiles. Help docs reworded (tabs). New DOM test for
profilerListSwitch. SW cache v81 -> v82.

frontend/sw.js

@@ -1,4 +1,4 @@
-const CACHE = 'otaman-v81';
+const CACHE = 'otaman-v82';
 const URLS = [
   'index.html',
   'help.html',