Add order-based party roster, back-navigation in battle selection, fix win-state cutscene leak

- Battle selection menu can now go back a fighter to re-decide their move,
  and battle win/loss no longer leaks the round's remaining queued move
  cutscenes into the ending state (cutsceneSystemDiscardQueued).
- Party roster is now driven by party.jsonc: every defined member always
  exists (partyInit), while party->order alone determines who's currently
  active - partyAddMember/partyRemoveMember (and their cutscene items) now
  activate/deactivate an existing roster member by index instead of
  creating/destroying one, with removal compacting order to stay packed.
- New PARTY_ADD_MEMBER/PARTY_REMOVE_MEMBER/PARTY_HEAL_MEMBER/PARTY_HEAL_ALL
  cutscene items.
- saveSlotInit/partyInit now return errorret_t and take their target
  struct directly (saveslot_t*/party_t*) instead of implicitly operating
  on SAVE.slot; saveSlotReadJSON resets through saveSlotInit rather than
  duplicating the reset logic.
- Test coverage: stub the JSON asset loader in save test fixtures so
  partyInit's real party.jsonc load runs against an in-memory doc instead
  of hanging with no asset system initialized.

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

test/save/savetestfixture.h

@@ -35,3 +35,21 @@ int saveTestFixtureTeardown(void **state);
  * filesystem permission tricks. Must be called after saveTestFixtureSetup.
  */
 void saveTestFixtureBlockSaveDirectory(void);
+
+/**
+ * Stubs the JSON asset loader's sync callback to hand back a small
+ * in-memory party.jsonc-shaped doc instead of doing a real file/zip read -
+ * saveInit()/saveSlotInit() seed the party roster via partyInit(), which
+ * loads party.jsonc through the real asset system, and there's no real
+ * asset bundle available under the test harness. No thread, no real I/O.
+ * Resets ASSET to a fresh, otherwise-empty state each call, so it's safe
+ * to call once per test. Called automatically by saveTestFixtureSetup.
+ */
+void saveTestFixtureStubPartyAsset(void);
+
+/**
+ * Frees the in-memory doc created by saveTestFixtureStubPartyAsset. Safe
+ * to call even if that function was never called. Called automatically
+ * by saveTestFixtureTeardown.
+ */
+void saveTestFixtureUnstubPartyAsset(void);