polish(access-control): apply the second cleanup round

- indent the nested auth-mode field so it lines up under its toggle's label
  instead of reading as a sibling row, and label the dropdown for screen readers
- order Chat right after Deploy Tabs so the three deploy targets stay adjacent
- flush the trailing Select All chips on the providers and platform rows
- drop the doubled margin on the name error (SettingRow already gaps it)
- hoist PLATFORM_FEATURES and PLATFORM_CATEGORY_ORDER to module scope
- drop the useCallback on the two save/discard handlers; nothing observes their
  identity and their deps changed on every keystroke anyway
- fix a comment that still pointed at a 'Hide Chat' toggle that no longer exists

Author: waleedlatif1