fix(frontend): download SQLite backup/export in web mode (#688)

[AtomicTrxn]

Description

Fixes self-hosted web backup/export flow for SQLite so users receive a browser download instead of only a server-side filename.

Root cause:

• Web backup_database already returned { filename, data } from backend.
• Frontend web paths (useExportData and useBackupRestore) ignored data and treated result as server-only save.

Fix summary:

• Web SQLite paths now call openFileSaveDialog(data, filename) and treat success as local save.
• Updated web backup/export copy to match actual behavior.
• Added regression tests for both hooks covering web SQLite download behavior.
• Includes rustfmt baseline fix for unrelated upstream file (crates/core/src/addons/tests.rs) to satisfy current Rust Check gate.

Note: Backend/API unchanged (POST /utilities/database/backup already returns data and filename).

Test Evidence

• cargo fmt --all -- --check ✅
• pnpm --filter frontend test -- use-export-data ✅
• pnpm --filter frontend test -- use-backup-restore ✅
• pnpm run build:types && pnpm --filter frontend type-check ✅

Fixes #688

Checklist

• I have read and agree to the Contributor License Agreement.

By submitting this PR, I agree to the CLA.