Add error logs viewer

[symonbaikov]

Summary

• add a Settings -> Error Logs dialog for local error history by day
• store error-only daily logs under the app log directory with 14-day retention
• capture backend Rust/plugin error logs plus frontend console.error, window.error, and unhandledrejection
• update log capture docs with the new in-app viewer flow

Details

• Added Tauri IPC commands for listing log days, reading a selected day, and recording frontend errors.
• Added an error-only tauri-plugin-log dispatch target that writes backend/plugin errors to daily files.
• Added a frontend installer that preserves existing console logging while forwarding error events to the backend without recursive failures.
• Added focused tests for backend retention/date validation, the dialog, Settings entry point, and frontend error forwarding.

Screenshots

Captured locally before creating the PR:

• Before: /tmp/openusage-error-logs-pr/screenshots/error-logs-settings-before.png
• After: /tmp/openusage-error-logs-pr/screenshots/error-logs-settings-after.png

Validation

• BINDGEN_EXTRA_CLANG_ARGS=-isystem/usr/lib/clang/21/include cargo test --manifest-path src-tauri/Cargo.toml error_logs --lib
• bun run test -- src/components/error-logs-dialog.test.tsx src/pages/settings.test.tsx src/lib/frontend-error-logging.test.ts
• bun run build
• cargo fmt --manifest-path src-tauri/Cargo.toml --check
• git diff --check

Notes

• No README provider-list update needed; this is not a plugin change.
• Visual screenshots were taken from Vite previews for Settings before/after. The full Tauri dev app was also launched successfully during manual validation on a temporary port because 1420 was already in use by another project.