Expose exclude_issue_numbers on gitea_allocate_next_work, remove excluded
numbers before ranking, normalize decoded-list and JSON-string
candidates_json fail-closed, and return candidate-set fingerprints for
dry-run/apply CAS. Same-owner leases on excluded issues surface a
structured resume/release blocker.
Closes#776
Co-Authored-By: Claude Opus 4.8 (1M context) <[email protected]>
