Add Apple Silicon macOS builds

[shriram-svg]

Summary

• configure macOS Electron Builder output to produce universal dmg and zip artifacts
• update Electron Builder within the existing 22.x range so universal macOS packaging is supported
• keep the existing boost-note-mac.dmg and boost-note-mac.zip artifact names for release/download URLs

Fixes #864.

Verification

• npx npm@6 ci --no-audit
• Electron Builder config validation via app-builder-lib/out/util/config.validateConfig
• ./node_modules/.bin/prettier --check package.json
• npx npm@6 run lint
• npx npm@6 run test-api -- --runInBand
• git diff --check

Note: local install used Node 25, so optional fsevents@1.2.13 emitted native build errors but npm exited 0; project CI is configured for Node 12.

AI-assisted with Codex; I reviewed the diff and validation output before submitting.

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