Per deep-review verdict SHIP-WITH-FIXES on PR #2636:
1. Profile-switch reconciliation: _refreshProfileSwitchBackground now re-fetches
/api/settings and re-applies hidden_tabs for the new profile. Without this,
Profile A's hidden-tabs choice stayed in effect under Profile B until the
user opened Settings → Appearance.
2. A11y: switched chips from role=button + aria-pressed to role=switch +
aria-checked. The pressed/not-pressed wording confused screen-reader users
because chip-off looks like the off state. Added role=group +
aria-labelledby on the container, and a :focus-visible style on the chips.
3. Server-side belt-and-suspenders: api/config.py now strips 'chat' and
'settings' from hidden_tabs at validation time, matching the client's apply-
time filter. A tampered POST can no longer persist the forbidden values.
3 new regression tests added (chat/settings rejection, profile-switch wiring,
chip a11y attributes).
Co-authored-by: FrancescoFarinola <francesco.farinola@example.com>