Add usage history export

[symonbaikov]

Description

Adds local usage history export for OpenUsage provider snapshots.

The app now stores successful usage snapshots locally and lets users export a selected date range as CSV or XLSX. XLSX exports include both a Summary sheet and a raw Snapshots sheet. The summary includes snapshot timestamps so provider metrics like Today, Yesterday, and Last 30 Days are clearly tied to when OpenUsage collected them.

History starts accumulating after this feature is installed. It is not retroactive provider history.

Related Issue

N/A

Type of Change

• Bug fix
• New feature
• New provider plugin
• Documentation
• Performance improvement
• Other (describe below)

Testing

• npm run test -- src/components/panel-footer.test.tsx src/App.test.tsx
• BINDGEN_EXTRA_CLANG_ARGS=-isystem/usr/lib/clang/21/include cargo test --manifest-path src-tauri/Cargo.toml local_http_api --lib
• npm run build

Notes

• Adds tauri-plugin-dialog for save-file dialogs.
• Adds rust_xlsxwriter for real .xlsx output.
• Keeps the existing /v1/usage API unchanged.
• Retains local history for the last 365 days.