feat(api): typed add_events(iter); generify internal path over T

Public API gains:

  History::add_events<I: IntoIterator<Item = Event<T, K>>>(events)
      -> Result<(), InferenceError>

which accepts the typed Event<T, K> shape added in Task 10. Ranks
from Outcome::Ranked are mapped to the legacy "higher f64 = better"
results internally.

add_events_with_prior now takes Vec<T> for times (was Vec<i64>),
generifying the whole internal path over T in a single fully-generic
impl<T: Time, D: Drift<T>, O: Observer<T>, K> block. The i64-specific
block is gone; record_winner/record_draw are now generic over T.

add_events_with_prior stays pub (not pub(crate)) because the ATP
example calls it directly with pre-built Index-based composition;
the new typed add_events is the primary public API going forward.

In-crate tests updated to call add_events_with_prior with an empty
HashMap. tests/api_shape.rs added with 3 integration tests covering
bulk ingest, draw, and mismatched-outcome error.

Part of T2 of docs/superpowers/specs/2026-04-23-trueskill-engine-redesign-design.md.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

tests/api_shape.rs

@@ -0,0 +1,84 @@
+//! Tests for the new T2 public API surface: typed add_events(iter) and the
+//! fluent event builder (added in Task 16).
+
+use smallvec::smallvec;
+use trueskill_tt::{ConstantDrift, ConvergenceOptions, Event, History, Member, Outcome, Team};
+
+#[test]
+fn add_events_bulk_via_iter() {
+    let mut h = History::builder()
+        .mu(0.0)
+        .sigma(2.0)
+        .beta(1.0)
+        .p_draw(0.0)
+        .drift(ConstantDrift(0.0))
+        .convergence(ConvergenceOptions {
+            max_iter: 30,
+            epsilon: 1e-6,
+        })
+        .build();
+
+    let events: Vec<Event<i64, &'static str>> = vec![
+        Event {
+            time: 1,
+            teams: smallvec![
+                Team::with_members([Member::new("a")]),
+                Team::with_members([Member::new("b")]),
+            ],
+            outcome: Outcome::winner(0, 2),
+        },
+        Event {
+            time: 2,
+            teams: smallvec![
+                Team::with_members([Member::new("b")]),
+                Team::with_members([Member::new("c")]),
+            ],
+            outcome: Outcome::winner(0, 2),
+        },
+    ];
+
+    h.add_events(events).unwrap();
+    let report = h.converge().unwrap();
+    assert!(report.converged);
+    assert!(h.lookup(&"a").is_some());
+    assert!(h.lookup(&"b").is_some());
+    assert!(h.lookup(&"c").is_some());
+}
+
+#[test]
+fn add_events_draw() {
+    let mut h = History::builder()
+        .mu(25.0)
+        .sigma(25.0 / 3.0)
+        .beta(25.0 / 6.0)
+        .p_draw(0.25)
+        .drift(ConstantDrift(25.0 / 300.0))
+        .build();
+
+    let events: Vec<Event<i64, &'static str>> = vec![Event {
+        time: 1,
+        teams: smallvec![
+            Team::with_members([Member::new("alice")]),
+            Team::with_members([Member::new("bob")]),
+        ],
+        outcome: Outcome::draw(2),
+    }];
+    h.add_events(events).unwrap();
+    h.converge().unwrap();
+}
+
+#[test]
+fn add_events_rejects_mismatched_outcome_ranks() {
+    use trueskill_tt::InferenceError;
+    let mut h: History = History::builder().build();
+    let events: Vec<Event<i64, &'static str>> = vec![Event {
+        time: 1,
+        teams: smallvec![
+            Team::with_members([Member::new("a")]),
+            Team::with_members([Member::new("b")]),
+        ],
+        outcome: Outcome::ranking([0, 1, 2]), // 3 ranks but 2 teams
+    }];
+    let err = h.add_events(events).unwrap_err();
+    assert!(matches!(err, InferenceError::MismatchedShape { .. }));
+}