swarm-ui: don't break at a narrow viewport

Closes #3447.

- Shell.css: .shell-header and .shell-nav wrap onto a second line
  below a breakpoint instead of forcing horizontal overflow — no
  hamburger/collapse menu, per mara's own 'don't break, don't
  over-invest' scoping.
- LinksMenu.css: bumped .links-menu-button and .links-menu-item to the
  same 2.75em (~44px, WCAG 2.5.5) touch-target floor the shared ui/
  kit's form controls and buttons already carry — this trigger is
  bespoke, not built from that kit, but the floor applies regardless.
- Table.tsx/.css: wrapped the table in a .ui-table-scroll container
  (overflow-x: auto) so a wide table scrolls within its own box on a
  narrow viewport instead of forcing the whole page to overflow
  horizontally — not named in the issue's two concrete spots, but the
  same 'should not break' failure mode, and fixing it at the shared
  Table primitive covers every future caller.

.create-agent-input's fixed width -> max-width was already fixed as
part of #3448's form kit.

Verified: tsc clean, build succeeds, screenshotted at 320px (hives
nav wraps, table scrolls internally, page itself doesn't overflow)
and 480px (create-agent form fields fit).

frontend/packages/swarm-ui/src/ui/table/Table.css

@@ -1,3 +1,8 @@
+/* Scrolls horizontally within its own box on a narrow viewport instead
+   of forcing the whole page to overflow — see Table.tsx's comment. */
+.ui-table-scroll {
+  overflow-x: auto;
+}
 .ui-table {
   width: 100%;
   border-collapse: collapse;

frontend/packages/swarm-ui/src/ui/table/Table.tsx

@@ -3,6 +3,12 @@
 // their own cell rendering rather than this component knowing about
 // any particular row shape, so it stays reusable for the swarm-wide
 // agent roster later without a rewrite.
+//
+// Wrapped in a scrollable container rather than letting a wide table
+// force the whole page to overflow horizontally on a narrow viewport —
+// a `<table>` doesn't shrink below its content's natural width on its
+// own, so without this the page itself would break, not just look
+// cramped.
 import type { ComponentChildren } from 'preact';
 import './Table.css';
 
@@ -22,23 +28,25 @@ export function Table<T>({
   rowKey: (row: T) => string;
 }) {
   return (
-    <table class="ui-table">
-      <thead>
-        <tr>
-          {columns.map((c) => (
-            <th key={c.key}>{c.header}</th>
-          ))}
-        </tr>
-      </thead>
-      <tbody>
-        {rows.map((row) => (
-          <tr key={rowKey(row)}>
+    <div class="ui-table-scroll">
+      <table class="ui-table">
+        <thead>
+          <tr>
             {columns.map((c) => (
-              <td key={c.key}>{c.render(row)}</td>
+              <th key={c.key}>{c.header}</th>
             ))}
           </tr>
-        ))}
-      </tbody>
-    </table>
+        </thead>
+        <tbody>
+          {rows.map((row) => (
+            <tr key={rowKey(row)}>
+              {columns.map((c) => (
+                <td key={c.key}>{c.render(row)}</td>
+              ))}
+            </tr>
+          ))}
+        </tbody>
+      </table>
+    </div>
   );
 }