hub/app: late answers stay on the page that asked; tokens per message

[ohdearquant]

Late answers and retry tokens on the resident page.

• Each navigation is a new page, a return to the same resident included. A control's or a send's answer that arrives after the page changed shows its result as a toast and leaves the page now shown alone: no panel is closed, no reload, the text being typed is kept. Before, a late answer for resident A closed B's open panels, and going A to B and back to A let it reload A and clear the new text.
• An unsent message keeps its token by resident, subject and words, so a newer message to the same resident no longer takes the older one's token; the same words again replay the first send instead of mailing twice.
• A control with no answer keeps its token, keyed by resident, action and arguments, so asking the same again is replayed by the server's once cache; an answered control frees it.

Tokens live in the page: a full reload starts with none, so a retry after a reload mints a new token.

The page script has no tests in this repository. It was checked with a script-level harness driving the page with delayed answers: every case above holds on this branch, and the previous page script fails five of them.

Stacked on #15; the base moves to main once #15 merges.