v0.1.20

Release notes:

• Fix Notes workspace sync flushing for create/delete/metadata/folder operations.
• Add create/delete sync stress coverage and harden switching stress selectors.
• Refresh Notes mobile launcher icon with a smaller foreground mark.
• Bump server and Notes Android version to 0.1.20.

Validation:

• cargo test --manifest-path backend/Cargo.toml
• npm run check --workspace @og-suite/notes
• npm run build --workspace @og-suite/suite
• Android signed APK verified with apksigner.
• Server Docker image smoke-tested on /api/v1/system/version.