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/networking/net_echo.ludic

@@ -9,16 +9,16 @@
 program NetEcho {
   entry {
     let out = bytes(4)
-    out[0] = 10
+    out[0] = '\n'
     out[1] = 20
     out[2] = 30
-    out[3] = 42
+    out[3] = '*'
     net_send(0, out, 4)                  # onto the wire (the built-in loopback)
 
     let inb = bytes(64)
     let n = net_poll(inb, 64)            # take the next datagram back off
     print(n)                             # 4
     var i = 0
-    while i < n { print(inb[i]);  i = i + 1 }   # 10 20 30 42
+    while i < n { print(inb[i]);  i += 1 }   # 10 20 30 42
   }
 }