Build v3 desktop foundation

[andreanjos]

Summary

• Adds the v3 desktop Audio Package Manager foundation: Tauri app, GUI workspaces, local service sidecar/supervisor, shared engine/service/model substrate, and audio-AI manifest/store foundation.
• Adds macOS preview and public release tooling, Desktop Release workflow, release evidence/checksum packaging, signed/notarized release gates, and GitHub release readiness/status helpers.
• Adds docs for architecture, local service contract, desktop product plan, macOS distribution/runbook/handoff, and v3 readiness.

Verification

• cd apps/apm-desktop && npm test
• cd apps/apm-desktop && npm run open:macos:preview -- --dry-run
• cd apps/apm-desktop && npm run open:macos:preview:dmg -- --dry-run
• cd apps/apm-desktop && npm run verify:v3:local
• cd apps/apm-desktop && npm run release:macos:status -- --repo andreanjos/apm --tag v0.1.1 --markdown --untracked-files all
• git diff --check && git diff --cached --check

Release Notes

Local preview app/DMG artifacts are verified and runnable, but public release remains blocked until:

• .github/workflows/desktop-release.yml is merged to the default branch
• macos-desktop-release GitHub Environment secrets are configured
• v0.1.1 is moved/recreated for the merged release commit
• a signed publish=false Desktop Release run passes release:macos:workflow-accept