feat(battleship): frontend on SDK v2 + vs-bot via gameKit

[Aaron1924]

Two stacked changes to Battleship's frontend, both on the SDK battleship.v2 protocol. Base is feat/battleship-commit-reveal (the SDK v2 / PR #106) — merge that first, then this can be rebased onto dev-raid.

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Part 1 — Migrate frontend/agent/bench off battleship.v1 (Merkle) → SDK battleship.v2

The SDK now owns the canonical commit-reveal Battleship (single board-hash commit + terminal legal-fleet reveal_board). The frontend still ran its own v1 (Merkle root + per-cell-salt per-shot proofs), so the legal-fleet fix wasn't live and the bench measured v1. This repoints every consumer to the SDK, keeping the existing game design (bot/pvp modes, many games per tunnel with a fresh fleet each game, manual placement, smart bot, resume).

• Move shapes → v2 (kind): commit{commitment} (raw Uint8Array), shoot{cell}, answer{isHit, next?}, terminal reveal_board{board, salt}. No type:/merkle/proveCell/per-cell-salt anywhere.
• Single-salt secret: FleetSecret { board, salt, commitment }; salts from crypto.getRandomValues(16).
• Per-game silent terminal reveal: vs-bot auto-reveals both boards at game end then rematches with a fresh fleet; PvP serializes the two terminal reveals A-then-B so the seats never propose at the same nonce.
• Migrated: engine/selfPlay.ts, protocol/multiGameBattleship.ts (battleship.multi.v2), agent/games/battleship/kit.ts (battleship.v2), engine/pvpDriver.ts, battleshipResumeAdapter.ts, view.ts+engine/bot.ts (type repoint), useBattleship.ts, useBattleshipPvp.ts.
• Deleted: protocol/battleship.ts (v1) + engine/merkle.ts (+ tests). loadbench Dockerfile drops the SDK-backed protocol COPY.

Part 2 — Route vs-bot through the gameKit (kit = single bot-move source)

Battleship was the only arena game whose solo/vs-bot UI did not route through its gameKit (every other game does; PvP is bespoke in all of them, incl. blackjack v1 on dev). This unifies it, mirroring Quantum Poker's pokerSelfPlay.ts.

• kit.BattleshipBot.plan is now the single source of commit/answer/reveal_board/shoot for vs-bot + bench. New games/battleship/battleshipSelfPlay.ts (makeSeatBot / stepBattleshipAuto / stepBattleshipWithHuman / applyHumanShot / isHumanShootTurn / runBattleshipSelfPlayToEnd) is a thin wrapper.
• Per-seat pipeline flag on the kit bot (default true): the human seat A is built pipeline:false (bare answers → the human fires its own shot); the bot seat B + bench are pipeline:true (folds the return shot for TPS).
• useBattleship.ts drives via two kit bots (rebuilt each game with the fresh fleet); the human's shot goes through applyHumanShot. Deleted the duplicate engine/selfPlay.ts#nextMove/playToCompletion/DrivenMove.
• PvP untouched (useBattleshipPvp.ts / engine/pvpDriver.ts have zero production diff) — matches every game's bespoke-PvP convention.

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Tests

• tsc --noEmit green; battleship + gameKit suite passes (38/38 after Part 1; 43/43 after Part 2).
• Engine tests drive real games via kit bots over a mock multi-game tunnel (balance conservation + decisive 17-hit terminal). Manual two-tab PvP + vs-bot multi-game smoke confirmed.

Out of scope (follow-ups)

• The Quantum-Poker "auto lane" / persistent bots / human-takeover / Auto-mode window (descoped).
• Tier-2 ZK legal-placement.