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/input_edge.ludic

@@ -19,9 +19,9 @@ program InputEdge {
 
   handler In phase Update {
     var v = 0
-    if Input.key_down('k')     { v = v + 1 }       # held
-    if Input.key_pressed('k')  { v = v + 10 }      # went down this frame
-    if Input.key_released('k') { v = v + 100 }     # went up this frame
+    if Input.key_down('k')     { v += 1 }       # held
+    if Input.key_pressed('k')  { v += 10 }      # went down this frame
+    if Input.key_released('k') { v += 100 }     # went up this frame
     print(v)
   }
 }