Port the special battle types and contest battles

Run the forced-shiny, trap, forced-item, Celebi, Suicune, roaming and Bug-Catching Contest battle types. Roaming battles keep their struct's DVs and HP byte, and every other battle makes CleanUpBattleRAM's roaming roll. The contest shows PARKBALL×, counts down Park Balls, ends when they run out, keeps its catch outside the party and asks before switching. Scripts load the special types with loadvar, and while a contest runs, encounters use BugCatchingContestBattleScript and ContestMons.

Validated with 596 unit tests, 155 browser tests (including the contest menu and switch screen), native/reference builds and reference/vendor/release checks. National Park's contest event, the roaming release and the Ilex Forest Celebi event come with their maps.

Closes #28

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/NATIVE_PORT.md

@@ -263,8 +263,16 @@ set it. A status heal after a full turn therefore penalises a paralysed
 or burned enemy again, as the original does. Kurt's balls keep their
 documented bugs (Heavy Ball bank, Fast Ball's three bytes, Moon Ball's
 BURN_HEAL compare, Love Ball's same gender). The Heavy Ball is refused for
-Kadabra and Sunflora, whose original weight read runs into VRAM. The
-Bug-Catching Contest's Park Ball count and contest Pokémon remain gaps.
+Kadabra and Sunflora, whose original weight read runs into VRAM.
+
+Special battle types follow `LoadEnemyMon`, `TryToRunAwayFromBattle`,
+`BattleMenu`, `CheckContestBattleOver`, `PokeBallEffect`,
+`BugContest_SetCaughtContestMon` and `BattleEnd_HandleRoamMons`. The
+contest's Park Balls and caught Pokémon (`BugContest`) and a roaming
+Pokémon's struct (`RoamMon`) are passed in and updated by the battle. The
+world keeps the contest in its script state while one runs, and switches
+encounters to `BugCatchingContestBattleScript` and `ContestMons`. It has
+no roaming Pokémon yet.
 
 `engine/pokemon/stats_screen.asm`: the stats screen's three pages (HP,
 status, types, experience to the next level; item and moves with PP; ID,