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;