ci: publish benchmarks in repository Pages

[cpunion]

Summary

• use the benchmark publisher default same-repository pages storage
• rely on the workflow-scoped github.token instead of an external-data PAT
• publish under the namespaced benchmark/baseline site path, leaving the Pages root available for other sites

Validation

• migrated the existing benchmark history to cpunion/llgo:pages
• enabled branch-based Pages at https://cpunion.github.io/llgo/
• reran publisher 30747761848, attempt 2: it pushed 5cd2067, updated PR [Based on #2255] runtime/ffi: use direct ffi_call_go where compatible #136 in place, and removed the persistent-publishing warning
• parsed both workflow and benchmark YAML; git diff --check passes

The new benchmark/baseline path is configured in this PR; after it is merged, the next publisher run will write the history at:

https://cpunion.github.io/llgo/benchmark/baseline/

[gemini-code-assist]

Caution

The consumer version of Gemini Code Assist on GitHub has been sunset. All code review activity has officially ceased.