Fix Gen 1/2 battle, menu, PC and audio parity gaps; wire luacheck into CI

CLOSES #1484, CLOSES #1486, CLOSES #1513, CLOSES #1517, CLOSES #1556, CLOSES #1564, CLOSES #1567

src/import/RomExtractorGen2.lua

@@ -5151,6 +5151,7 @@ function RomExtractorGen2:extractMenuGfx()
   }
   out.pack = pack
   out.pokedex = self:pokedexGfx()
+  out.billsPc = self:billsPcGfx()
   out.pokegear = self:pokegearGfx()
   out.trainerCard = self:trainerCardGfx()
   out.unownPuzzle = self:unownPuzzleGfx()
@@ -5697,6 +5698,25 @@ function RomExtractorGen2:pokedexGfx()
   return dex
 end
 
+-- BillsPC_InitGFX's four tiles at vTiles2 $5c
+-- (engine/pokemon/bills_pc.asm:2170-2173)
+function RomExtractorGen2:billsPcGfx()
+  if not self.symbols["PCMailGFX"] then return nil end
+  local pc = {}
+  local gfx = self:symbol("PCMailGFX")
+  self:write2bpp(self.rom:bytes(gfx.bank, gfx.address, 4 * 16),
+    32, 8, "pc/mail_item.png")
+  pc.icons = "assets/generated/pc/mail_item.png"
+  pc.firstTile = 0x5c
+  pc.palette = self:predefPal(PREDEFPAL_POKEDEX)
+  -- gfx/pc/orange.pal
+  if self.symbols["BillsPCOrangePalette"] then
+    local orange = self:symbol("BillsPCOrangePalette")
+    pc.orangePalette = self:colors(orange.bank, orange.address, 4)
+  end
+  return pc
+end
+
 -- Reads a `tile, count` RLE tilemap (Pokegear_LoadTilemapRLE).  The routine's
 -- own comment says "repeat count, tile ID" and has it backwards: it loads b
 -- from the first byte, c from the second, and writes `b` c times.  $ff ends

src/import/RomImporter.lua

@@ -146,6 +146,9 @@ local VERSION_REQUIRED_FILES_OVERRIDE = {
     -- complete and SlotMachine crashed on its labelled-cell fallback.
     "assets/generated/slots/gold_slots_1.png",
     "assets/generated/card_flip/card_flip_1.png",
+    -- PCMailGFX (engine/pokemon/bills_pc.asm:2170-2173): Bill's PC has no
+    -- held-item or mail icon in a cache built before the symbol was listed.
+    "assets/generated/pc/mail_item.png",
   },
 }
 -- Same Gen 2 extract, so a Silver cache is complete when the same files exist.