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>

runtime/native/reflect_io.ludic

@@ -32,11 +32,11 @@ function reflect_serialize(e: int) -> Val {
         var node = value_int(raw)
         if world_field_type(p, f) == "fixed" { node = value_fixed(raw) }
         value_put(comp, fname, node)
-        f = f + 1
+        f += 1
       }
       value_put(obj, world_prop_name(p), comp)
     }
-    p = p + 1
+    p += 1
   }
   return obj
 }
@@ -49,7 +49,7 @@ function reflect_apply(e: int, v: Val) -> int {
   var i = 0
   while i < value_count(v) {
     let pname = value_key_at(v, i)
-    if pname[0] != 64 {                            # skip reserved "@…" keys
+    if pname[0] != '@' {                            # skip reserved "@…" keys
       let p = world_prop_id(pname)
       if p >= 0 and world_has(e, p) != 0 {
         let comp = value_at(v, i)
@@ -59,13 +59,13 @@ function reflect_apply(e: int, v: Val) -> int {
           let f = world_field_id(p, fname)
           if f >= 0 {
             world_set(e, p, f, value_as_int(value_at(comp, j)))
-            set = set + 1
+            set += 1
           }
-          j = j + 1
+          j += 1
         }
       }
     }
-    i = i + 1
+    i += 1
   }
   return set
 }