LOMP - Limited Offline Mode Paper

Fixed: plugin silently did nothing on 1.21.x Paper builds. Both channel injection paths failed at startup, so allow-listed players still went through Mojang auth and got "failed to verify username".

• Paper injection: corrected API signature (Key + ChannelInitializeListener)
• Spigot fallback: handle Mojang-mapped ServerConnectionListener
• Fixed crash on dual IPv4/IPv6 binds
• Injection failure now logs loudly instead of silently no-op