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/light_tiers.ludic

@@ -69,7 +69,7 @@ program LightTiers {
     dark()
     Light.clear_normals()
     Light.normal(18, 30, 8, 8, 0.7, 0.0)       # this patch faces right (toward the light)
-    Light.normal(46, 30, 8, 8, 0.0 - 0.7, 0.0) # this patch faces left (away)
+    Light.normal(46, 30, 8, 8, 0.0 - 0.7, 0.0)  # this patch faces left (away)
     Light.point(32, 34, 44, 16777215, 1.0)     # a light centred between the patches
     let toward = lum(22, 34)              # patch facing the light
     let away   = lum(48, 34)              # patch facing away