Merge pull request '[SPA][P8] #180 Next-round + final leaderboard flow i Angular SPA' (#185) from dev/issue-180-spa-next-round-final-leaderboard-v2 into main

docs/ISSUE-180-SPA-NEXT-ROUND-FINAL-LEADERBOARD-EVIDENCE.md

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+# Issue #180 Evidence — SPA next-round + final leaderboard
+
+## Flow log (Angular SPA)
+1. Host reaches `reveal` phase and runs `loadScoreboard()` (`GET /lobby/sessions/:code/scoreboard`).
+2. Host can start next round directly in SPA via `startNextRound()` (`POST /lobby/sessions/:code/rounds/next`) and then session hydrate (`GET /lobby/sessions/:code`) without page reload.
+3. Host can finish game directly in SPA via `finishGame()` (`POST /lobby/sessions/:code/finish`), rendering final leaderboard payload in the same shell.
+4. Player SPA renders final leaderboard from refreshed finished-session payload (sorted by score desc, nickname tiebreak) without leaving SPA route.
+5. Error/retry paths are implemented and covered:
+   - scoreboard failure -> `scoreboardError` + retry button
+   - next-round failure -> `nextRoundError` + retry button
+   - finish-game/final-leaderboard failure -> `finishError` + retry button
+
+## Test evidence
+### `frontend/angular` (Vitest)
+- `src/app/features/host/host-shell.component.spec.ts`
+  - `runs next-round transition without reload and clears scoreboard payload`
+  - `captures finish-game failure for retry and stores final leaderboard on success`
+- `src/app/features/player/player-shell.component.spec.ts`
+  - `builds final leaderboard in finished status without legacy page hop`
+
+Result:
+- Test Files: 2 passed
+- Tests: 9 passed
+
+### `frontend` shared SPA tests (regression)
+Result:
+- Test Files: 5 passed
+- Tests: 24 passed