macOS code signing + notarization

[ikseong00]

Goal

Sign and notarize the macOS build so users no longer have to right-click → Open to bypass Gatekeeper.

Why

Friction for first-time users. The current unsigned dmg flow scares non-developers ("damaged / unidentified developer"). Notarization removes the warning.

Acceptance

• electron-builder build.mac set with hardenedRuntime: true, gatekeeperAssess: true, entitlements: build/entitlements.mac.plist.
• CI builds use env vars (CSC_LINK, CSC_KEY_PASSWORD, APPLE_ID, APPLE_APP_SPECIFIC_PASSWORD, APPLE_TEAM_ID) as secrets.
• Released .dmg passes spctl --assess --type install without warning on a fresh mac.
• CONTRIBUTING / release docs explain how to set up the cert + Apple ID for new maintainers.

Hints

• Requires Apple Developer Program membership ($99/yr).
• Reference: https://www.electron.build/code-signing.html
• entitlements file likely needs com.apple.security.network.client (statusLine HTTP) and optionally com.apple.security.files.user-selected.read-write (no — pet only writes to userData).

Blockers

• Apple Developer cert availability. Until owner registers, this issue stays open.