Modularize live baseline runner

[yvette-carlisle]

Summary

• Convert live_baseline_elf into a normal directory-backed bin root.
• Split checks, backfill, runtime, types, and provider logic into focused modules behind facade files.
• Keep existing external call sites and behavior intact while removing ad-hoc path wiring.

Validation

• cargo make check after checks split: passed, including nextest 403 passed / 92 skipped.
• cargo make check after backfill split: passed, including nextest 403 passed / 92 skipped.
• cargo make check after runtime split: passed, including nextest 403 passed / 92 skipped.
• cargo make check after types split: passed, including nextest 403 passed / 92 skipped.
• cargo make check after providers split: passed, including nextest 403 passed / 92 skipped.
• Read-only skeptic review: pass_with_notes, no blockers.

Diff Size

• 29 files changed, 1602 insertions, 1564 deletions.