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>

examples/games/platformer_scaffolding.ludic

@@ -34,13 +34,13 @@ program PlatformerScaffolding {
   @OnSpawn(Spike) handler SI { }
 
   var picked: int = 0
-  @On(ItemPickedUp) handler OnPick { picked = picked + 1 }
+  @On(ItemPickedUp) handler OnPick { picked += 1 }
   var sprang: int = 0
-  @On(Sprang) handler OnSpring { sprang = sprang + 1 }
+  @On(Sprang) handler OnSpring { sprang += 1 }
   var hurt: int = 0
-  @On(Hurt) handler OnHurt { hurt = hurt + 1 }
+  @On(Hurt) handler OnHurt { hurt += 1 }
 
-  function tick_n(n: int) -> void { var i = 0;  while i < n { tick_fixed();  i = i + 1 } }
+  function tick_n(n: int) -> void { var i = 0;  while i < n { tick_fixed();  i += 1 } }
   function bi(b: bool) -> int { if b { return 1 };  return 0 }
 
   entry {