fix(chat): gate the message actions on the edit and delete windows

[bmc08gt]

The edit and delete windows arrived in ResolvedUserFlags in #1397 with nothing reading them. Four fixes on top of that, three of them user-visible.

The windows now gate the menu

MessagePolicy carries both windows and ChatViewModel maps the resolved flags into it, so the selection bar stops offering Edit or Delete on a message past its window instead of sending a request the server answers CANNOT_EDIT / CANNOT_DELETE.

Capabilities resolve once, when a transcript row is mapped, and the windows keep running under an open transcript. So the ToggleMessageSelection reducer re-applies them to the bubble it selects. Resolver and reducer share withinWindows, and a test pins that both give the same answer for the same instant.

A just-sent message would not long-press

Sending writes an optimistic row with event_sequence 0 — only the server can stamp it — and confirmPendingMessage updated the id, timestamp, unread sequence and status but not the sequence. The row stayed at 0 until some later fetch of the chat overwrote it, which is why leaving the chat and coming back appeared to fix it.

Anything keyed on that stamp read the message as unacknowledged in the meantime: resolveCapabilities returns nothing for sequence 0, so the row was not selectable, and expected_event_sequence is validated >= 1 on the wire, so an edit or delete built from the stale value could not have been valid either. The confirm now writes the sequence the send echo carries.

The bottom bar sat behind the keyboard

Screens are drawn edge to edge, so the window is not resized when the IME opens and the bottom-aligned bar slid up underneath it. An edit failure, raised while the composer still holds focus, showed an error the user could not see. imePadding on the animated content lifts the bar; the scrim still covers the whole window.

Both windows are overridable

Watching the menu narrow otherwise means waiting out whatever the server publishes. Both are now Fields on the User Flags screen, entered in seconds like the bill exchange timeout above them.