PD-5388 restore the record summary link on records with no public information - #2927

…ormation

A record with no publicly visible information still has a creation date and a
last-modified date, but the header's show/hide toggle was gated on
`noDisplayableData`, so a visitor had no way to reach either. `summary.json`
serves an empty record on its active path, so the Key dates panel was already
there to show — nothing but the gate was missing.

`canToggleRecordSummary` replaces that gate and refuses only records that do
not exist. The two projected label spans lose their own `*ngIf`: they render
inside the toggle button, so gating them left an icon with no text.

Copy iD and print keep their `noDisplayableData` gate — the ticket asks for the
summary link alone — and a unit test pins that boundary so a future change has
to mean it.

Locked, deprecated and deactivated records are a separate ticket: their
`summary.json` short-circuits before the dates are read, so un-hiding the
toggle there opens a blank panel.

Also null-guards the three `userInfo` conditions in record-info, which renders
on this same empty-record path before `userInfo` has resolved.