Split knowledge source DTOs

[yvette-carlisle]

Summary

• Move knowledge source fetch parameters and source row DTOs into types/sources.rs
• Keep knowledge page write DTOs and KnowledgePageSearchRow in the parent types.rs facade
• Preserve the existing knowledge::types and elf_storage::knowledge re-export surfaces

Validation

• cargo make fmt-rust
• cargo make fmt-rust-check
• cargo make check-rust
• cargo make lint-vstyle
• git diff --check
• cargo make lint-rust
• cargo make test-rust (370 passed, 92 skipped)
• cargo make check (370 passed, 92 skipped)
• cargo make test-rust-integration (92 passed, 370 skipped)
• cargo make check-trace-gate
• Read-only scout and skeptic reviews