XY-1062: [ELF AMK P1] Extend Source Library capture for URL, thread, file, and source-span authority

[yvette-carlisle]

Summary

• Adds normalized Source Library capture metadata with stable source record ids and source span refs.
• Preserves source capture as evidence only; docs_put remains separate from approved Memory Authority.
• Records typed policy spans for excluded/redacted content and exposes stable span ids through search/excerpt hydration.
• Updates the owning source-ref specs for the new capture and pointer contract.

Validation

• cargo make fmt
• cargo make lint-fix
• cargo make checks (333 passed, 89 skipped)
• cargo nextest run -p elf-service --test acceptance --run-ignored only (54/54 passed)

Review

• Independent fresh-context review found one blocking span-id round-trip issue.
• Repair commit aligns chunk-id excerpt hydration with captured chunk source-span ids.
• Independent repair-verification review is clean for HEAD 499199a.