Make desktop updates architecture-aware and add chat action dismissal/deletion UX

[rexlManu]

Summary

• Add desktop runtime architecture detection and include runtime arch metadata in update state.
• Improve macOS Apple Silicon behavior when running Intel builds by disabling differential downloads and surfacing a Rosetta warning in the sidebar.
• Harden external URL handling by centralizing safe URL validation and routing blocked window opens to trusted external links only.
• Preserve legacy desktop user data directories while standardizing new userData path names.
• Add project action deletion flow in chat header controls with confirmation dialog and success/error toasts.
• Make thread error banners dismissible and keep plan follow-up send behavior synchronized with interaction mode updates.
• Include supporting test updates for desktop update state/runtime metadata and UI warning logic, plus small platform/test reliability fixes.

Testing

• Not run (bun lint)
• Not run (bun typecheck)
• Updated/added unit checks for desktop update state transitions and runtime metadata propagation.
• Updated/added UI logic checks for Intel-on-Apple-Silicon warning visibility and warning copy behavior.