Gate (Codex) caught two SILENT regressions in the original fix: explicitly
hiding the header in the 'else'/'empty' branches also hid populated read views.
- _setMemoryHeaderButtons('read') now shows the header for ALL read views
(incl. read-only Project Context / External Notes), gating only the Edit btn.
- _renderProfileConceptHelp() now uses a new 'help' header mode (shows header,
hides all action buttons) instead of 'empty' (which hid the help title).
Adds tests/test_issue4891_detail_header_visibility.py (proven non-vacuous).
Co-authored-by: luandnh <luandnh@users.noreply.github.com>