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/library/world_bounds.ludic

@@ -8,7 +8,7 @@
 program WorldBounds {
   import "ludic.core/components.ludic"
 
-  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 }
 
   function clear_all() -> void {
@@ -57,7 +57,7 @@ program WorldBounds {
     tick_n(1)
     var live = 0
     var q = World.query_next(PBody, 0)
-    while q >= 0 { live = live + 1;  q = World.query_next(PBody, q + 1) }
+    while q >= 0 { live += 1;  q = World.query_next(PBody, q + 1) }
     print(live)                                      # 0 — the out-of-bounds body was killed
   }
 }