* Improve built-in browser downloads
Implements docs/browser-normal-download-behavior.md with automatic OS Downloads saving, collision-safe destinations, and renderer download controls.
* Clean up browser downloads on tab closure and guest destruction
- Cancel and drop pending download records when webview guests are destroyed or closed to prevent memory leaks and dangling state.
- Purge tracking entries for cancelled downloads lacking an active tab.
- Document filename normalization and reservation assumptions in download builder.
- Translate "Copy Terminal ID" context menu action in Spanish and Chinese locales.
Jinjing