Harden exports, persistence, and query efficiency

[11sid11]

What changed

• Fix derived ZIP people summaries so Split activity is scoped to the correct trip and canonical Split/Lend balance rules are reused.
• Preserve exact currency precision in CSV/ZIP exports, including zero- and three-decimal currencies.
• Build JSON backups and ZIP packages from read-only IndexedDB snapshots.
• Use existing Track/person indexes and map-based grouping to reduce repeated full-table and per-group scans.
• Move Settings/Search raw DB reads behind query/repository boundaries.
• Make Lend ledger delete/restore cascades atomic and add rollback coverage.
• Tighten generic repository table typing.
• Improve startup/onboarding/settings error handling and remove destructive storage-reset guidance.
• Simplify Data & Storage copy so portable backups vs CSV exports are clearer.
• Add modal focus entry, focus trapping, and focus restoration.

Why

A codebase audit found one real export correctness bug plus several contained data-consistency, efficiency, and UX ambiguities. This PR fixes those findings without changing the app architecture, financial schema, dependencies, or module independence.

Regression coverage

• multi-trip Split balances in ZIP people summary
• JPY/KWD/INR export precision
• Lend cascade rollback on write failure
• modal focus lifecycle
• month range helper behavior

Expected checks

• typecheck
• lint
• unit/integration tests
• production build