Make the source pass the CI lint

The central pipeline lints where the old inline one did not, and it
aborts on any warning. Nothing here was actually wrong: 166 of the 243
warnings were the TIC-80 API and the game's own globals being undeclared,
which is what .luacheckrc is for — the same shape impostor already uses.

The rest was trailing whitespace on 14 lines, now stripped. INPUT_KEY_X
is unused but kept: it belongs to the LEFT/RIGHT/A/B/X/Y set and removing
it would leave a gap in the mapping, so luacheck is told to allow the
family.

Verified locally by merging the sources the way the pipeline does and
running luacheck over the result: 0 warnings, 0 errors.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

inc/system/system.main.lua

@@ -45,7 +45,7 @@ function init_game()
 end
 
 function TIC()
-  init_game() 
+  init_game()
 
   cls(Config.colors.black)
   local handler = STATE_HANDLERS[Context.active_window]