[refactor] Replace hardcoded values with build flags and cleanup duplicates.

- Add #ifndef guards for pin defines duplicated between platformio.ini and main.cpp
- Use DEFAULT_LOOK_AHEAD, DEFAULT_BRIGHTNESS, DEFAULT_IDLE_TIMEOUT, DEMO_RESET_PAUSE
  build flags instead of hardcoded magic numbers
- Add WIFI_SSID build flag for configurable access point name
- Remove unused build flags (BRIGHTNESS, IDLE_TIMEOUT, DEBOUNCE_DELAY)
- Remove progressive difficulty / evolution feature (getDynamicPly)
- Replace goto with structured control flow in performAiMove
- Deduplicate checkGameEnd win/draw branches
- Implement blunder mode: configurable chance (%) to pick a random column,
  preserving instant win/block detection

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

platformio.ini

@@ -12,14 +12,12 @@ build_flags =
     -D ENC_SW=2
     -D SENSITIVITY=4
     -D SHOW_BORDER=0
-    -D BRIGHTNESS=25
-    -D IDLE_TIMEOUT=45000
     -D DEMO_RESET_PAUSE=20000
-    -D DEBOUNCE_DELAY=50
     -D DEFAULT_LOOK_AHEAD=8
     -D DEFAULT_BRIGHTNESS=25
     -D DEFAULT_IDLE_TIMEOUT=45
     -D MAX_GAME_LOG=100
+    -D WIFI_SSID=\"Connect4\"
     -D WIFI_PASSWORD=\"youlose4\"
 lib_deps =
     fastled/FastLED @ 3.9.12