feat: add revision-fenced warmth plans

[haasonsaas]

Summary

• add deterministic budgeted warmth planning to the CLI and JSON-lines server
• rank direct, related, repo-map, and heat candidates with a typed schema
• export only clean single-repository shards whose indexed bytes match the exact Git tree
• bound inputs and serialized plans and document the consumer contract

Verification

• cargo fmt --all -- --check
• cargo clippy --all-targets --all-features (repository baseline warnings only; no new warmth warnings)
• cargo test (412 passed)
• Bazel unavailable locally; required hosted checks must pass before merge

Companion consumer: evalops/orb#415.