Refactor: Move buzzer sound handling to class members, tune sounds,

[alco28]

This PR introduces the following improvements:

• Refactored buzzer sound handling: all RTTTL melodies are now class members (startup_song, shutdown_song, message_song, discovery_song, channel_song, ack_song) in the buzzer class for better maintainability and reuse.
• Slightly tuned the channel and ack buzzer sounds for clearer and more consistent user feedback.
• Added a PlatformIO build task to tasks.json for convenient building directly from within VS Code.
• Replaced all hardcoded RTTTL strings in the codebase with these class members, allowing centralized management and easier future adjustments of buzzer sounds.

No changes to board configuration files are included in this PR. This refactor improves code clarity, maintainability, and user experience.