refactor(api): rename Player to Rating

The struct holds prior/beta/drift — a rating configuration, not a
person. The person-with-temporal-state is the Competitor (renamed in
the next task). Resolves Player/Agent ambiguity.

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

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

benches/batch.rs

@@ -1,7 +1,7 @@
 use criterion::{Criterion, criterion_group, criterion_main};
 use trueskill_tt::{
-    BETA, GAMMA, KeyTable, MU, P_DRAW, SIGMA, agent::Agent, batch::Batch, drift::ConstantDrift,
-    gaussian::Gaussian, player::Player, storage::AgentStore,
+    BETA, GAMMA, KeyTable, MU, P_DRAW, Rating, SIGMA, agent::Agent, batch::Batch,
+    drift::ConstantDrift, gaussian::Gaussian, storage::AgentStore,
 };
 
 fn criterion_benchmark(criterion: &mut Criterion) {
@@ -17,7 +17,7 @@ fn criterion_benchmark(criterion: &mut Criterion) {
         agents.insert(
             agent,
             Agent {
-                player: Player::new(Gaussian::from_ms(MU, SIGMA), BETA, ConstantDrift(GAMMA)),
+                player: Rating::new(Gaussian::from_ms(MU, SIGMA), BETA, ConstantDrift(GAMMA)),
                 ..Default::default()
             },
         );