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/grid.ludic

@@ -45,12 +45,12 @@ program Grid {
       let dx = p[i].x - p[i - 1].x
       let dy = p[i].y - p[i - 1].y
       var ad = dx
-      if ad < 0 { ad = 0 - ad }
+      if ad < 0 { ad = -ad }
       var ay = dy
-      if ay < 0 { ay = 0 - ay }
+      if ay < 0 { ay = -ay }
       if ad + ay != 1 { ok = false }
       if Grid.blocked(p[i].x, p[i].y, '#') { ok = false }
-      i = i + 1
+      i += 1
     }
     if ok { print(9) }
 
@@ -58,7 +58,7 @@ program Grid {
     if len(Grid.a_star(1, 1, 3, 2, '#')) == 0 { print(10) }   # (3,2) is a wall
     if Grid.blocked(3, 2, '#') { print(11) }
     if not Grid.blocked(1, 1, '#') { print(12) }
-    if Grid.blocked(0 - 1, 0, '#') { print(13) }              # out of bounds
+    if Grid.blocked(-1, 0, '#') { print(13) }              # out of bounds
   }
 
   handler Run phase Update { quit() }