fix(ui): give the mobile refresh controls labels and full width

At <=640px the RAG "Sync sources" pill and the History "Refresh"
pill squeezed down to tiny icon-only buttons — hard to discover and
tap on a phone. They are now full-width labeled pills:

- the RAG page-head row wraps so the Sync pill drops below the
  "Knowledge base" title at full width; the History page-head
  already wrapped the pill below its title block
- the Sync label's min(16rem, 40vw) cap lifts on mobile (min-width: 0
  engages the ellipsis) so the live-file text truncates against the
  full width instead of the 40vw cap
- the Refresh glyph joins its visible label (it stays hidden on
  desktop, where the label carries the pill)

This matches the established mobile full-width pill language (New
chat / Share / stale-ban Regenerate). The three unit tests that
pinned the old icon-only CSS are updated to pin the new behavior.

tests/unit/test_hamburger_nav.py

@@ -326,7 +326,6 @@ def test_mobile_menu_rows_are_comfortable_targets() -> None:
     for untouched in (
         ".new-chat-label { display: none; }",
         ".auth-label { display: none; }",
-        ".sync-label { display: none; }",
         ":root { --header-h: 58px; }",
     ):
         assert untouched in mobile, f"the ≤640px block lost {untouched!r}"