fix: align route graphics gapX/gapY model

[han4wluc]

Summary

• update the shared layout/control element model to use gapX and gapY instead of gap
• update schema-1 and schema-2 compatibility fixtures plus the compat generator to reflect the current container contract
• bump the package patch version to 1.2.4

Testing

• bunx vitest run tests/model-api.test.js
• bun run test:compat