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/coverage.ludic

@@ -16,7 +16,7 @@ program CoverageSpec {
       return 1
     }
     if n < 0 {
-      return 0 - 1
+      return -1
     }
     return 0
   }
@@ -35,7 +35,7 @@ program CoverageSpec {
 
   test "sign covers every branch" {
     expect_eq(sign(7), 1)
-    expect_eq(sign(0 - 3), 0 - 1)
+    expect_eq(sign(-3), -1)
     expect_eq(sign(0), 0)
   }