Give the sidebar groups, and tidy the tables, disclosures and tab bar

The desktop sidebar is now grouped: Queue, On-call, Alerts and Stats; Team
and Admin; then Account at the foot, shown as the signed-in person with an
avatar and their name. The active item has a bar as well as a tint. The
queue's row of team chips is gone: the team selector is the one place the
team is chosen, and the chips offered the same choice a second time.

Tables get 16px between columns, so a right-aligned count no longer touches
the text beside it. An empty SSO group reads "Not configured" instead of a
dash, and the main action on each of those pages (New source, New switch,
Add member, Assign, and the admin Add, Create invite and Create) is a filled
button, with Edit and Cancel staying secondary. The bare triangles on
"Grouped by" and the label lists are real disclosure buttons: a chevron
that turns and a 44px target on a touch screen.

On a phone the More tab was a <button> that kept the browser's grey box, so
it looked highlighted next to four plain links. It now matches them, the
labels are 12px and the open tab's icon is filled.

Web UI only: no endpoint or JSON shape changed, so nothing to mirror in
terdut-tui.

internal/web/static/index.html

@@ -110,6 +110,9 @@
         <svg viewBox="0 0 24 24" aria-hidden="true"><path d="M4 20h16M7 20v-7M12 20V6M17 20v-10"/></svg>
         <span class="nav-label">Stats</span>
       </a>
+      <!-- Dividers between the groups (Queue, On-call, Alerts, Stats | Team,
+           Admin | Account). Desktop sidebar only; the phone bar has no room. -->
+      <span class="nav-sep" aria-hidden="true"></span>
       <a class="nav-link" href="/team" data-section="team" aria-label="Team">
         <svg viewBox="0 0 24 24" aria-hidden="true"><circle cx="9" cy="8" r="3"/><circle cx="17" cy="9" r="2.5"/><path d="M3 19a6 6 0 0 1 12 0M15 19a5 5 0 0 1 6-4"/></svg>
         <span class="nav-label">Team</span>
@@ -121,9 +124,14 @@
         <svg viewBox="0 0 24 24" aria-hidden="true"><path d="M12 3l7 3v6c0 4-3 7-7 9-4-2-7-5-7-9V6z"/></svg>
         <span class="nav-label">Admin</span>
       </a>
-      <a class="nav-link nav-link-secondary" href="/more" data-section="more" aria-label="Account">
+      <span class="nav-sep nav-sep-account" aria-hidden="true"></span>
+      <!-- At the foot of the desktop sidebar, as the signed-in person: app.js
+           fills the avatar and the name from /api/me, and until then it reads
+           "Account". -->
+      <a class="nav-link nav-link-secondary nav-account" href="/more" data-section="more" aria-label="Account">
         <svg viewBox="0 0 24 24" aria-hidden="true"><circle cx="12" cy="8" r="3.5"/><path d="M5 20a7 7 0 0 1 14 0"/></svg>
-        <span class="nav-label">Account</span>
+        <span class="nav-avatar" id="nav-avatar" aria-hidden="true" hidden></span>
+        <span class="nav-label" id="nav-account-label">Account</span>
       </a>
       <!-- Phone-width only (see .nav-more-btn in app.css): opens the same
            sheet the old hamburger button did, for the sections the bottom