refactor(runtime,packages,examples): named constants, package enums, idiom sweep

- runtime: HEADLESS_FRAME_PATH, STICK_DEADZONE / STICK_LEFT_X/Y, key and
  byte codes as char literals throughout (`k == 'w'`, `fill(rt_map, ' ', …)`)
- ludic.gameplay/stats: drop the duplicate `stat_field` (it answered "atk"
  for every build stat); Stats.base uses stats_field_name
- ludic.shooter: compare aim modes and fire patterns with AimMode.* and
  WeaponPattern.* instead of raw ints; STICK_RIGHT_X/Y
- ludic.npcai: DecisionMade / brain_set_state use AiState.*
- examples/games/menu.ludic uses Font.load / Ui.* with FONT_PATH and
  BACKDROP named; strings.ludic header says what it prints
- whole tree: `x = x + 1` → `x += 1` (single-term right-hand sides only),
  `0 - x` → `-x`, ASCII codes → char literals; every .ludic and every
  ```ludic fence reformatted with the fixed formatter (whitespace only)

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

runtime/native/systems_tileskin.ludic

@@ -43,9 +43,9 @@ function esys_tileskin() -> void {
           if is_atlas != 0 { atlas_draw_ex(sprite, tx * size, ty * size, sc, 0, 0) }
           else { rt_draw_sprite_ex(sprite, tx * size, ty * size, sc, 0, 0) }
         }
-        tx = tx + 1
+        tx += 1
       }
-      ty = ty + 1
+      ty += 1
     }
     e = World.query_next(P, e + 1)
   }