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.

web/src/model.rs

@@ -47,6 +47,54 @@ pub struct MoveView {
     pub scopa: bool,
 }
 
+#[derive(Debug, Clone, Copy, Deserialize)]
+pub struct TeamCounts {
+    #[serde(rename = "A")]
+    pub a: i32,
+    #[serde(rename = "B")]
+    pub b: i32,
+}
+
+#[derive(Debug, Clone, Copy, Deserialize)]
+#[allow(dead_code)]
+pub struct TeamBools {
+    #[serde(rename = "A")]
+    pub a: bool,
+    #[serde(rename = "B")]
+    pub b: bool,
+}
+
+/// Which team (if any) won each scoring category of a hand.
+#[derive(Debug, Clone, Deserialize)]
+pub struct Award {
+    #[serde(default)]
+    pub carte: Option<String>,
+    #[serde(default)]
+    pub denara: Option<String>,
+    #[serde(default)]
+    pub settebello: Option<String>,
+    #[serde(default)]
+    pub primiera: Option<String>,
+}
+
+/// The scoring breakdown of one completed hand.
+#[derive(Debug, Clone, Deserialize)]
+#[allow(dead_code)]
+pub struct HandSummary {
+    pub cards: TeamCounts,
+    pub denara: TeamCounts,
+    pub settebello: TeamBools,
+    pub primiera: TeamCounts,
+    pub scope: TeamCounts,
+    pub award: Award,
+    #[serde(default)]
+    pub hand: i32,
+    #[serde(default)]
+    pub team_a_points: i32,
+    #[serde(default)]
+    pub team_b_points: i32,
+}
+
 #[derive(Debug, Clone, Deserialize)]
 #[allow(dead_code)]
 pub struct GameView {
@@ -74,6 +122,16 @@ pub struct GameView {
     pub seats_open: Option<usize>,
     #[serde(default)]
     pub last_move: Option<MoveView>,
+    /// Scoring breakdown of the most recent hand (present once a hand has
+    /// been completed).
+    #[serde(default)]
+    pub last_hand: Option<HandSummary>,
+    /// Seats that acknowledged the hand-end summary.
+    #[serde(default)]
+    pub acknowledged: Vec<usize>,
+    /// ISO-8601 instant at which the next hand is dealt automatically.
+    #[serde(default)]
+    pub hand_end_deadline: Option<String>,
     #[serde(default)]
     pub your_turn: Option<bool>,
     /// Legal captures per hand card; present only for the player on turn.