Add all-or-nothing multi-target claims

[Deicyde]

Extracted from #115 so the claim transport can be reviewed independently. The exact head 21328e99 is merged with current main; #137 has removed the former README baseline blocker.

Summary

• let autoform claim acquire, renew, and release accept several targets
• read every target with one ls-remote, apply the existing per-key ownership checks, and update every ref in one git push --atomic
• attach one --force-with-lease to every ref so a lost race changes none of the batch
• report every known blocker in input order, including malformed leases, while preserving the exact single-target path and output
• refuse remotes without atomic-push support instead of falling back to partial updates

This supplies the deadlock-free primitive used by the later shared-declaration revision contract; workers acquire the whole target set or none.

Validation

• focused claims and CLI suites: 95 passed
• Ruff and git diff --check: clean
• range-diff matches the reviewed Open statements and a revision contract for shared Lean declarations #115 commits exactly
• exact-head GitHub Python 3.10/3.13, Windows, real Lean, and CLA: all pass

[Deicyde]

Exact-head review is complete at d7384653. The batch path preserves the single-key contract, reads all refs once, validates every lease before writing, uses one atomic push with a force-with-lease per ref, refuses unsupported atomic remotes, and reports malformed or contended keys without partial ownership.

Focused claims/CLI tests pass; the branch-push Python, Windows, and real-Lean jobs are green. The PR-merge Python failure is solely the stale README assertion on current main and is fixed by #137. No claim-transport blocker remains; merge #137 first.

[Deicyde]

The refreshed exact head 21328e99 is fully green against current main: Python 3.10/3.13, Windows, real Lean, and CLA all pass. The atomic multi-target claim primitive is mergeable and no longer order-blocked.