XY-1017 Build Source Library ingest and benchmark gate

[yvette-carlisle]

Summary

• add Source Library profile validation for doc source refs, including source kind, canonical URI, timestamps, trust labels, and locator checks
• return docs_search_l0 hash aliases and chunk position locators for hydration
• add source_library benchmark fixtures, make tasks, docs, and an ignored external integration guard that docs_put does not create Memory Notes

Validation

• cargo make check
• cargo make real-world-memory-source-library
• cargo test -p elf-service source_library
• cargo test -p elf-service docs_l0_pointer
• cargo test -p elf-eval --test real_world_job_benchmark source_library