[codex] Bump version to 2.1.1

[rz-openai]

Summary

• Bump the application version from 2.1.0 to 2.1.1.
• Advance the release build number to 20260618.01.
• Keep the Electron package and lockfile versions synchronized with VERSION.

This is an independent version-only PR. Version 2.1.0 was tagged but never produced a successful release build, so the next release should use a new patch version rather than moving the existing tag.

Release ordering

• Merge [codex] Restore arm64 macOS release packaging #160 before cutting the 2.1.1 release.
• Do not tag 2.1.1 until the combined main branch passes the full release archive workflow.

Testing

• npm ci
• npm run format:check
• npm run lint
• npm run typecheck
• npm test
• npm run build
• JAVA_HOME=/Library/Java/JavaVirtualMachines/temurin-17.jdk/Contents/Home ./gradlew --no-daemon build
• xcodebuild -project Snap-O.xcodeproj -scheme Snap-O CODE_SIGNING_ALLOWED=NO CODE_SIGNING_REQUIRED=NO build
• Built and ran Snap-O locally
• Added or updated tests (not applicable: version metadata only)

The full release archive preflight is deferred until #160 lands, because this branch is intentionally independent from that release-build fix.

Checklist

• I have read the Contributing guidelines
• Documentation has been updated (not applicable)