fix(drive): skip property-less sheets in has_sheet_titled

[newhoggy]

Summary

• Spreadsheet::has_sheet_titled compared against Sheet::title(), which coerces a sheet with absent properties to "", causing a false collision with an explicit empty-title request.
• Restore the pre-refactor behavior (filter_map(properties.as_ref()), matching structure.rs::resolve_sheet's hand-written check) so property-less sheets are skipped, not coerced.
• Add a regression test covering a property-less sheet alongside a normal one.

Fixes #1702

Test plan

• cargo test --lib drive::sheets::types — 13 passed, including the new has_sheet_titled_skips_a_property_less_sheet
• cargo clippy -- -D warnings
• cargo fmt --check

[github-actions]

Coverage

Total: 97.28% ⚪ 0 pp vs main

Comparing fe55042..848d954 (merge-base → PR head)

File	Before	After	Δ
src/drive/sheets/types.rs	98%	98.15%	🟢 0.15 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	882-885	both	guards this test helper against misuse; every call site below passes an acquire subcommand
src/cli/drive/lease.rs	ignore	896-899	both	guards this test helper against misuse; every call site below passes a prune subcommand
src/drive/lease/ledger.rs	ignore	666-670	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	977-981	both	every test using this double refuses before authenticating; a hit here is a regression, not a coverage gap

Patch coverage

Patch: 100% (13/13 new lines covered)

File	Patch	Uncovered new lines
src/drive/sheets/types.rs	100% (13/13)	—

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