🧹 Refactor instruments to use BaseSynth abstract class

[Pitrat-wav]

This PR introduces a major architectural improvement by consolidating common instrument logic into a new BaseSynth abstract class.

Key Changes:

• New BaseSynth Class: Provides a unified interface for all instruments, including:
  • initialized state tracking.
  • Standardized outputGain node (supporting both Tone.Volume and Tone.Gain).
  • setVolume(db: number) with smooth rampTo interpolation to prevent audible clicks.
  • dispose() method for cascading resource cleanup.
• Instrument Refactoring: AcidSynth, FMBass, HarmSynth, PadSynth, DrumMachine, and SamplerInstrument now inherit from BaseSynth. Internal Tone.js nodes are lazily initialized via a standardized init() method.
• Initialization Synchronization: Updated audioStore.ts to call init() for all instruments during the main audio setup, ensuring that outputGain nodes are ready before they are wired to the mixer channels.
• Consistent API: Consumers like GlobalSequencer.ts now interact with instruments through a more predictable and type-safe API, replacing direct property mutations with base class methods.

Benefits:

• Reduced Duplication: Eliminates repetitive boilerplate for volume, init-flags, and disposal.
• Audio Quality: Standardizes the use of parameter ramping for volume changes.
• Maintainability: Makes it significantly easier to implement new instruments by following the BaseSynth contract.
• Memory Management: Ensures consistent disposal of audio nodes across all instrument types.

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PR created automatically by Jules for task 4338946224554170690 started by @Pitrat-wav

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