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/ecs/hello.ludic

@@ -19,8 +19,8 @@ program Hello {
   # runs once per match, each property bound by name and self() giving that entity.
   @Queries(these: [Pos, Vel])
   handler Move phase FixedUpdate {
-    Pos.x = Pos.x + Vel.dx
-    Pos.y = Pos.y + Vel.dy
+    Pos.x += Vel.dx
+    Pos.y += Vel.dy
   }
 
   handler Report phase Update {

examples/ecs/world_query.ludic

@@ -16,8 +16,8 @@ program WorldQuery {
     var sum   = 0
     var e = world_query_next(H, 0)
     while e >= 0 {
-      count = count + 1
-      sum = sum + world_get(e, H, hp)
+      count += 1
+      sum += world_get(e, H, hp)
       e = world_query_next(H, e + 1)
     }
     print(count)   # 2

examples/ecs/world_scan.ludic

@@ -19,10 +19,10 @@ program WorldScan {
     var e = 0
     while e < n {
       if world_kind(e) == Um {
-        count = count + 1
-        sum = sum + world_get(e, H, hp)
+        count += 1
+        sum += world_get(e, H, hp)
       }
-      e = e + 1
+      e += 1
     }
     print(count)   # 2
     print(sum)     # 110