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/numeric.ludic

@@ -14,7 +14,7 @@ program Numeric {
     if Huge.str(Huge.add(Huge.from(1000000000), Huge.from(1))) == "1.00e9" { print(6) }  # +1 negligible
     if Huge.cmp(Huge.from(1000000000), Huge.from(1000000)) == 1 { print(7) }
     if Huge.exp(Huge.mul(Huge.from(1000000), Huge.from(1000000))) == 12 { print(8) }
-    if Huge.str(Huge.from(0 - 42)) == "-4.20e1" { print(9) }
+    if Huge.str(Huge.from(-42)) == "-4.20e1" { print(9) }
     if Huge.str(Huge.from(0)) == "0" { print(10) }
 
     # --- Angle: wrapping radians (built on the deterministic Math.*) ---