Add core player model tests

[justinfernald]

Fixes #324

What changed

Replaced the complex-player-model coverage gap with six public-API behavioral tests covering:

• complete PlayerDto → PlayerModel → DTO round-tripping
• asynchronous waitForReady() resolution
• SmartPlayerModel state projection and typed per-player message routing
• reactive listener change detection and destruction cleanup
• PlayerStore join/update/kick lifecycle with stable model identity
• aggregate listeners for both existing and future players, including cleanup

The existing CI workflow already runs yarn coverage; this PR makes that gate exercise the player abstractions called out by the issue instead of only basic math smoke assertions.

Verification

• yarn vitest run test/src/player-models.test.ts — 6/6 passing
• yarn test --run — 5 files / 22 tests passing
• yarn coverage — 5 files / 22 tests passing
  • PlayerModel.ts: 100% lines
  • SmartPlayerModel.ts: 86.84% lines
  • PlayerStore.ts: 73.5% lines
• temporary no-reference strict TypeScript project covering src and the new test — passing
• eslint test/src/player-models.test.ts — passing
• yarn build — passing
• git diff --check — passing

The repository's stock yarn type-check fails identically on untouched master with TS6305 because vite.config.d.ts has not been built from the referenced vite.config.ts. The focused no-reference TypeScript verification above passed.

Demo

Screenshots and screencasts are not applicable because this PR adds automated non-visual library coverage only. Run yarn coverage to reproduce the test and per-file coverage evidence.