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.ui.lua

@@ -35,7 +35,7 @@ end
 function UI.word_wrap(text, max_chars_per_line)
     if text == nil then return {""} end
     local lines = {}
-    
+
     for input_line in (text .. "\n"):gmatch("(.-)\n") do
         local current_line = ""
         local words_in_line = 0
@@ -50,18 +50,18 @@ function UI.word_wrap(text, max_chars_per_line)
                 current_line = word
             end
         end
-        
+
         if words_in_line > 0 then
             table.insert(lines, current_line)
         else
             table.insert(lines, "")
         end
     end
-    
+
     if #lines == 0 then
         return {""}
     end
-    
+
     return lines
 end