Add hand-end scoring summary screen with acknowledgement

After each hand of an unfinished match the game now pauses in a new
hand_end phase instead of dealing immediately:

- engine: hand_points gains an 'award' map (which team won each category),
  _end_hand stops at hand_end with a deadline, new acknowledge_hand deals
  the next hand once all four players have acked; plays are rejected while
  the summary is up
- state: acked seats, hand_end_deadline and hand_ack_timeout are persisted
  and exposed in the personalized view (also on the finished state, so the
  final hand is explained before the result)
- ws: new {"action": "ack"}; a per-hand timer force-deals the next hand
  after HAND_ACK_TIMEOUT_SECONDS (new env var, default 30s) so an away
  player cannot stall the match
- web: modal explaining each category in plain language with icons (card
  images for denara/settebello/primiera), team-coloured rows, running
  totals with progress bars, an 'Understood — next hand' button that turns
  into 'Waiting for …' plus an auto-continue countdown; the final screen
  shows the last hand's breakdown too

Verified in the browser against the compose stack: hand played to
completion, summary rendered (including a carte tie), ack from all four
players dealt the next hand live, and the auto-continue path fired when
nobody acked. 60 backend tests + mypy + cargo tests green.

README.md

@@ -28,6 +28,15 @@ Because both the browser and the app talk to the OIDC issuer at
 echo "127.0.0.1 mockoauth" | sudo tee -a /etc/hosts
 ```
 
+## Between hands
+
+When a hand ends but the match is not decided, the game pauses on a
+**scoring summary screen**: every player sees how each category was won
+(carte, denara, settebello, primiera, scope) with the running totals and
+must click "Understood" before the next hand is dealt. If someone is away
+the next hand is dealt automatically after `HAND_ACK_TIMEOUT_SECONDS`
+(default 30s). The match-ending hand is explained on the final screen.
+
 ## Development
 
 Backend (from `server/`):