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/physics.ludic

@@ -20,7 +20,7 @@ program Physics {
     hit: int = 0, entered: int = 0, exited: int = 0
   }
 
-  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 }
 
   # despawn every live entity carrying a property, so each scenario starts clean.
@@ -65,7 +65,7 @@ program Physics {
     # re-apply the run velocity each frame, the way a controller drives it from
     # held input — so hit_wall stays asserted while pressed against the wall.
     var bi2 = 0
-    while bi2 < 80 { World.set(a, pb, f_vx, fixed(4));  tick_fixed();  bi2 = bi2 + 1 }
+    while bi2 < 80 { World.set(a, pb, f_vx, fixed(4));  tick_fixed();  bi2 += 1 }
     print(World.get(a, pp, f_x))                     # 284 — right edge stops at the wall (300)
     print(World.get(a, pb, f_hw))                    # 1   — hit_wall while pressed
     print(bi(World.get(a, pb, f_vx) == 0))           # 1   — the sweep zeroed it this frame
@@ -93,7 +93,7 @@ program Physics {
     spawn Plat { Position { x: 400, y: 150 }, Collider { w: 64, h: 8, one_way: 1 } }
     spawn Runner { Position { x: 405, y: 60 }, Body { gravity: fixed(1), max_fall: fixed(6) }, Collider { w: 16, h: 16 } }
     let e1 = World.query_next(pb, 0)
-    spawn Riser { Position { x: 430, y: 200 }, Body { vy: fixed(0 - 4), policy: 1 }, Collider { w: 16, h: 16 } }
+    spawn Riser { Position { x: 430, y: 200 }, Body { vy: fixed(-4), policy: 1 }, Collider { w: 16, h: 16 } }
     var e2 = World.query_next(pb, 0)
     if e2 == e1 { e2 = World.query_next(pb, e1 + 1) }
     tick_n(20)