Wire up battle AI/scene-return, reclaim cutscene item slots, fix GOTO

- battleStateSelectionAiDecide: AI-controlled fighters now actually
  queue a basic attack against the first living enemy instead of doing
  nothing every round.
- battleStateEndingInit: disposes the battle and switches back to
  SCENE_TYPE_OVERWORLD instead of leaving the game stuck in the battle
  scene forever.
- cutsceneSystemNext now pops each finished item off the front of the
  running cutscene (cutsceneRemoveFront) instead of leaving it in place
  forever, so a long-running cutscene (many battle rounds splicing
  items in repeatedly) no longer grows scene->items unboundedly.
- cutsceneGoTo reworked to match: since consumed items are evicted, a
  marker behind the current position can't be found in the live queue
  anymore, so it now re-parses the cutscene fresh from its source file
  (cutsceneLoadParse, into a persistent scratch buffer, not the stack)
  and replaces the live queue with marker-onward from that fresh parse.
  Only supported when the running cutscene is the one
  cutsceneSystemLoad/cutsceneCutsceneResolve populated.
- Fixed a real bug this surfaced: cutsceneSystemPrepare unconditionally
  cleared loadedFile, which ran *after* cutsceneCutsceneResolve had
  just stamped it but *before* the cutscene started - wiping it out
  immediately and breaking cutsceneGoTo for any cutscene entered via a
  CUTSCENE item or cutsceneCutsceneResolve (e.g. the main menu's
  NEW_GAME/OPTIONS/QUIT navigation). Now only cleared when switching
  away from loadedScene entirely.
- Added cutsceneLoadParse, the shared "lock asset, require loaded,
  parse items, unlock" sequence, replacing four near-identical copies
  across cutsceneSystemLoad/cutsceneCutsceneResolve/
  cutsceneInsertResolveAndSplice/battleStateExecutingInit. Each call
  site handles its own fatal-error display; cutsceneLoadParse itself
  just propagates.
- Added test_cutscene.c (cutsceneRemoveFront) and a regression test for
  the loadedFile bug. Writing the zero-count RemoveFront test caught a
  real self-move bug (count == 0 passed dest == src into memoryMove).

Co-Authored-By: Claude Sonnet 5 <[email protected]>

test/rpg/cutscene/CMakeLists.txt

@@ -6,6 +6,7 @@
 include(dusktest)
 
 # Tests
+dusktest(test_cutscene.c)
 dusktest(test_cutscenesystem.c)
 dusktest(test_cutscenecontrol.c)
 dusktest(test_cutscenemaparea.c)