fix(drive): absolutize --backup-dir at resolution time

[newhoggy]

Summary

• A relative drive lease --backup-dir is now absolutized before it's stored in the ledger — closing a bug where drive lease prune/restore run from a different cwd would resolve a relative backup dir against the wrong directory, silently orphaning real backups.
• Fixes fix(drive): relative --backup-dir is stored relative in the lease ledger; prune drops the row from another cwd #1692.

Test plan

• cargo build
• cargo test --lib drive::lease::settings:: (23 passed)
• cargo clippy --all-targets -- -D warnings

[github-actions]

Coverage

Total: 97.27% ⚪ 0 pp vs main

Comparing 5573c1a..3cbfa35 (merge-base → PR head)

File	Before	After	Δ
src/drive/lease/settings.rs	98.45%	96.86%	🔴 -1.58 pp

🔇 5 ignored region(s), 0 tolerated region(s)

ignore removes the lines from both reports; tolerate keeps them in the reported percentage but scores them against the baseline, so a cross-run flip cannot move a delta. Regions are read from each revision's own source.

File	Kind	Lines	Rev	Reason
src/cli/drive/lease.rs	ignore	408-412	both	a sheet restore's fresh backup is always a DriveCopy — restore.rs's own recheck refuses unless the target is still a spreadsheet, and acquire() only ever takes a Bytes backup of a non-native target; this arm exists solely for exhaustiveness over the shared LeaseBackup enum
src/cli/drive/lease.rs	ignore	928-931	both	guards this test helper against misuse; every call site below passes an acquire subcommand
src/cli/drive/lease.rs	ignore	942-945	both	guards this test helper against misuse; every call site below passes a prune subcommand
src/drive/lease/ledger.rs	ignore	812-816	both	mutate_locked refuses before ever calling the closure, so its body never runs — a hit here is a regression, not a coverage gap
src/drive/lease/restore.rs	ignore	1137-1141	both	every test using this double refuses before authenticating; a hit here is a regression, not a coverage gap

Patch coverage

Patch: 87.88% (29/33 new lines covered)

File	Patch	Uncovered new lines
src/drive/lease/settings.rs	87.88% (29/33)	141, 143, 145, 362

Uncovered new lines (4)

• src/drive/lease/settings.rs:141
• src/drive/lease/settings.rs:143
• src/drive/lease/settings.rs:145
• src/drive/lease/settings.rs:362

_{📦 Full per-file coverage summary · run summary}