Remove allowedSfxChannels functionality - allow SFX in all channels

- Remove allowedSfxChannels from database schema and all code
- Remove channel checking logic from all SFX commands (!sfx, /sfx, /soundboard)
- Remove /config sfxchannels subcommand
- Update config.json and example to remove channel restrictions
- Simplify SFX system to work in any channel with bot access

Benefits:
- Better user experience - no confusing channel restrictions
- Simpler configuration - fewer settings to manage
- Cleaner codebase - reduced complexity
- Universal access - SFX works anywhere the bot can send messages

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

src/config/config.js

@@ -102,7 +102,6 @@ class ConfigManager {
       internalName: "Unknown Guild",
       prefix: "!",
       enableSfx: true,
-      allowedSfxChannels: null,
       sfxVolume: 0.5,
       enableFunFacts: true,
       enableHamFacts: true,