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/tiled_p2.ludic

@@ -23,16 +23,16 @@ program TiledP2 {
     var n = 0
     var y = 0
     while y < 10 { var x = 0
-      while x < 16 { if rt_tile(x, y) == 35 { n = n + 1 };  x = x + 1 }
-      y = y + 1 }
+      while x < 16 { if rt_tile(x, y) == 35 { n += 1 };  x += 1 }
+      y += 1 }
     return n
   }
   function grid_hash() -> int {
     var h = 0
     var y = 0
     while y < 10 { var x = 0
-      while x < 16 { h = h * 31 + rt_tile(x, y);  x = x + 1 }
-      y = y + 1 }
+      while x < 16 { h = h * 31 + rt_tile(x, y);  x += 1 }
+      y += 1 }
     return h
   }
 
@@ -75,7 +75,7 @@ program TiledP2 {
     let f_grd = World.field_id(pb, "on_ground")
     let a = World.query_next(pb, 0)
     var i = 0
-    while i < 80 { tick_fixed();  i = i + 1 }
+    while i < 80 { tick_fixed();  i += 1 }
     if World.get(a, pp, f_y) == 112 { print(13) }      # feet rest on the tile floor top (128)
     if World.get(a, pb, f_grd) == 1 { print(14) }
   }