feat(mods): add battle menu auxiliary action

docs/rfcs/0007-battle-menu-auxiliary-actions.md

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+# RFC 0007: Battle menu auxiliary actions
+
+## Status
+
+Proposed.
+
+## Problem
+
+Tool mods can inspect/capture a persistent checkpoint only at a settled
+ordinary wild/trainer player-decision boundary. Before this proposal, that
+boundary had no public semantic input/action seam: `BattleState` consumed the
+command loop directly. A mod could reach it only through private battle/input
+internals, which would be unsafe and incompatible with controller/touch input.
+
+## Contract
+
+`mod.hooks:wrap("battle.menu_auxiliary", callback)` is called only when START
+is pressed at the existing checkpoint-safe player-decision boundary. The
+callback signature is:
+
+```lua
+function callback(next, game, context)
+  -- context is { kind = "wild" } or { kind = "trainer" }
+  -- return true after claiming START, otherwise return next(game, context)
+end
+```
+
+The context is data-only. No live battle controller, input object, serializer,
+or restoration primitive is exposed. A `true` result consumes START for that
+fixed step without selecting a battle command. With no installed handler,
+START is inert exactly as before. Hook priorities and error isolation are the
+existing generic wrapper semantics: a throwing handler is skipped and cannot
+advance battle state.
+
+The engine reuses the same internal safety predicate as battle checkpoint
+capture. Link, Safari, ghost/demo, unsupported origins, scripts, queues,
+animations, messages, forced replacement/locked actions, and unsettled HP or
+status presentation never invoke the hook.
+
+## Compatibility and verification
+
+The call is additive and no-op with no handler. ROM-free engine tests prove
+wild/trainer delivery, cursor/turn preservation, and unsafe-phase refusal;
+the mod-SDK fixture proves a loaded mod can consume the semantic action using
+only its public hook facade. `gate_hooks` automatically includes the new call
+site in no-mod parity coverage.