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/events/cancel.ludic

@@ -20,8 +20,8 @@ program Cancel {
 
     # the realistic shape: only apply the effect when the decision isn't vetoed
     var hp = 100
-    if emit BeforeHurt(amount: 8)  == 0 { hp = hp - 8 }    # allowed  -> 92
-    if emit BeforeHurt(amount: 50) == 0 { hp = hp - 50 }   # vetoed   -> unchanged
+    if emit BeforeHurt(amount: 8)  == 0 { hp -= 8 }    # allowed  -> 92
+    if emit BeforeHurt(amount: 50) == 0 { hp -= 50 }   # vetoed   -> unchanged
     print(hp)                                 # 92
   }
 }

examples/events/layer_events.ludic

@@ -17,7 +17,7 @@ program LayerEvents {
     }
     layer Ctrl {
       handler Drive phase LateUpdate {
-        step = step + 1
+        step += 1
         if step == 1 { disable layer Hud }           # frame 1: hide -> Hidden 2, Draw stops
         if step == 2 { enable layer Hud }            # frame 2: show -> Shown 1, Draw resumes
         if step == 3 { quit() }                      # frame 3: after Draw ran again

examples/events/mod_events.ludic

@@ -6,7 +6,7 @@ program ModEvents {
   var total: int = 0
   event Damage { amount: int = 0 }
   @On(Damage) handler Native { print(amount) }        # prints each hit
-  @On(Damage) handler Accum  { total = total + amount }   # sums them
+  @On(Damage) handler Accum  { total += amount }   # sums them
 
   entry {
     emit Damage(amount: 10)     # Native prints 10

examples/events/program_events.ludic

@@ -11,8 +11,8 @@ program ProgramEvents {
   @Public @OnStart handler Boot { print(1) }        # -> program_start
   @Public @OnQuit  handler Bye  { print(2) }        # -> program_quit
 
-  @On(program_start) handler ModInit { print(100) } # mod boots after the game
-  @On(program_quit)  handler ModDone { print(200) } # mod tears down as the game exits
+  @On(program_start) handler ModInit { print(100) }  # mod boots after the game
+  @On(program_quit)  handler ModDone { print(200) }  # mod tears down as the game exits
 
   handler Run phase Update { quit() }
 }

examples/events/recurse.ludic

@@ -11,7 +11,7 @@ program Recurse {
   event Ping { }
   event Pong { }
 
-  @On(Ping) handler A { n = n + 1; emit Pong() }   # each Ping deepens by one Pong
+  @On(Ping) handler A { n += 1; emit Pong() }   # each Ping deepens by one Pong
   @On(Pong) handler B { emit Ping() }              # ...and each Pong by one Ping
 
   entry {

examples/events/scoped.ludic

@@ -8,7 +8,7 @@ program Scoped {
   model Unit { Health }
   var fires: int = 0
   event Tick { }
-  @On(Tick) handler OnTick { for (Health) in query [Health, {Unit}] { fires = fires + 1 } }
+  @On(Tick) handler OnTick { for (Health) in query [Health, {Unit}] { fires += 1 } }
 
   entry {
     spawn Unit { Health { hp: 1 } }