feat(crash): make the crash game playable end-to-end

[netqo]

Summary

Wires Crash (CU-07) end-to-end: the third playable game and the first real-time one. Place a bet, watch the multiplier climb along an exponential curve, and cash out before it crashes (or set an auto-cashout target).

Rationale

Same round pattern as Coinflip/Mines, extended for a time-driven round:

• GameRepository.startCrash validates + debits the stake and draws the crash point on the C++/JNI engine (committed via the hash); settleCrash credits the payout on cash out and records the round. Reuses WalletRepository.applyRoundResult.
• CrashCurve is a pure, unit-tested exponential curve (e^(t/TAU)), kept out of the engine and ViewModel.
• CrashViewModel runs a ticker that samples the curve until the crash point, supporting manual cash out and an auto-cashout target. The live multiplier is a dedicated StateFlow<Double>, separate from the slow CrashUiState, so the per-frame ticker only recomposes the chart and the hero readout - the recomposition story the Profiler report will make for Crash.
• RoundDetailViewModel branches by game and rebuilds the cashout-vs-crash position bar (the crash-shaped detail) from the round's real seeds.
• Controls swap by phase (setup / live / result) and the finished round shows a compact result panel, so the weighted chart keeps its room and the layout stays stable on a cash out or a crash.

Verification

• ./gradlew testDebugUnitTest detekt ktlintCheck assembleDebug compileDebugAndroidTestKotlin green locally (JDK 17).
• New tests: CrashCurveTest, CrashViewModelTest (cash out settles a win; reaching the crash point settles a loss), startCrash/settleCrash cases in GameRepositoryImplTest.
• Installed the debug APK on a physical device: placed bets (stake debited), watched the multiplier climb smoothly, cashed out (payout credited), let rounds crash (stake lost), exercised the auto-cashout target. Confirmed the round shows in History and Round Detail with the position bar + real seeds, the Profile P&L includes Crash, and the layout stays stable across cash out / crash.

Test plan

• Place Bet debits the stake and starts the climbing multiplier.
• Cash Out credits stake x the current multiplier.
• Reaching the crash point loses the stake.
• An auto-cashout target cashes out at that multiplier (unless it crashes first).
• The round lands in History / Round Detail (with the position bar + real seeds) and the Profile P&L.
• The layout stays stable on cash out and crash; New Bet returns to setup.

Related issues

Refs the games-card work for the final entrega (Crash is the 3rd of 5 games).

Checklist

• Commit messages follow Conventional Commits (see CONTRIBUTING.md).
• Branch name follows the naming convention (feat/, fix/, chore/, etc.).
• The change is scoped: no unrelated edits sneaked into this PR.
• If user-visible behavior changed, CHANGELOG.md has been updated under [Unreleased].
• If a new dependency was added, it is justified in the PR description. (No new dependencies.)