Chat: 'is typing…', 'Seen by' and search #97

Parent

#91

What to build

• "Is typing…": while a chat person types, the others see "Anna is typing…" (or "Anna and Bram are typing…"). It is kept in the backend's memory and expires about 5 s after the last keystroke.
• "Seen by": on your own messages, "Seen by N", with the names on click. It counts only chat people (Members, the Product Owner, Guests) whose last read message is at or after it.
• Search: inside one chat, on message text and file names, with a From (person) filter and a Files only filter. Clicking a result scrolls to the message.

Spec stories 25, 28, 29.

Acceptance criteria

• POST /api/projects/{id}/chat/typing, typing names in the polling response (chat people only, not yourself)
• "Seen by" in the message data for the author
• GET /api/projects/{id}/chat/search?q=&from=&files_only=
• Frontend: typing line, Seen by with names, search panel with filters and jump-to
• API and NiceGUI tests

Blocked by

• Chat reactions and @mentions #96