Add zero-channel BlackHole variant with updated installation process

[un33k]

Description:

Summary

• Implements zero-channel BlackHole variant as an audio termination device (/dev/null for audio)
• Updates installation documentation to separate standard variants from the experimental 0ch variant
• Removes 0ch from standard installer build loop to prevent accidental distribution
• Adds dedicated installer script for 0ch variant with proper warnings

Changes

• Installer/create_installer.sh: Remove 0ch from standard build loop
• README.md: Add manual build instructions for 0ch variant with clear warnings
• scripts/create_0ch_installer.sh: New dedicated installer script for 0ch variant
• Previous commits added the core zero-channel driver implementation

Test plan

• [ ] Verify standard installers (2ch, 16ch, etc.) build correctly without 0ch
• [ ] Test manual 0ch build instructions work as documented
• [ ] Confirm 0ch installer script creates working package
• [ ] Validate 0ch variant appears as audio termination device in Audio MIDI Setup

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