Add tempfiles dashboard widget

[multiplex55]

Motivation

• Provide a dashboard widget to list and manage application temp files with configurable display count and refresh behavior.
• Reuse existing patterns for widgets that cache data, support manual/automatic refresh, and expose a settings UI.

Description

• Add src/dashboard/widgets/tempfiles.rs implementing TempfilesWidget with TempfilesConfig (limit, refresh_interval_secs, manual_refresh_only), caching via TimedCache, and UI for listing files, showing human-friendly names/aliases, and per-item/clear-all actions using crate::plugins::tempfile::list_files().
• Implement alias parsing in alias_for to extract user-provided aliases from filenames and present optional original filenames next to aliases.
• Provide actions: Add opens tempfile:dialog via add_action, per-item Clear triggers tempfile:remove:<path> via remove_action, and Clear all triggers tempfile:clear via clear_all_action.
• Register the new module in src/dashboard/widgets/mod.rs (mod tempfiles;, pub use tempfiles::TempfilesWidget;) and add a default factory entry in WidgetRegistry::with_defaults with TempfilesWidget::settings_ui.

Testing

• No automated tests were executed for this change.
• Manual compile/commit steps were performed during development (no cargo test run in this rollout).

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Codex Task