feat(updater): What's New update window with explicit actions; open Settings on current Space

[quiet-node]

Summary

Adds a dedicated "What's New" update window and routes every update entry point (chat footer, Settings banner, tray menu) through it so the user previews release notes and picks an action explicitly instead of an install starting on a single click. Also fixes the Settings panel to open on the user's current macOS Space (including over another app's fullscreen Space) instead of stranding it on Space 1.

Changes

• Update window (src/view/update/UpdateWindow.tsx, src/main.tsx, src/hooks/useUpdater.ts): editorial release-notes layout with four actions: Skip This Version, Remind Me Later, Install & Quit, Install & Restart. Markdown body + publish date from the updater manifest, GitHub-link fallback when notes are absent.
• Backend (src-tauri/src/updater/*, lib.rs): skip_update_version / open_update_window commands, persisted skipped_versions (back-compatible sidecar), should_surface_update decision helper, ThukiUpdatePanel NSPanel modeled on the overlay panel.
• Settings Space fix (lib.rs): settings/update panels use the proven overlay pattern (nonactivating + can_join_all_spaces, no activateIgnoringOtherApps) so they appear in-place on the current Space.

Review hardening (commit 50ed8d7)

• Removed unused core:window:allow-close capability (least-privilege: no frontend path calls window.close(); close is intercepted Rust-side and windows only hide()).
• UpdateWindow action handlers no longer silently swallow promise rejections: a shared runAction helper logs the failure and still closes the window so it cannot hang with no feedback.
• Corrected stale/contradictory panel doc comments (is_floating_panel, show_*_window activation notes, install_update_inner tray rationale).
• Removed em dashes from new comments per project writing-style rule.

Testing

• bun run test:all:coverage: 1314 frontend tests pass; backend llvm-cov 100% lines/functions/branches.
• bun run validate-build: clean (lint + clippy + format + typecheck + full build), zero warnings/errors.

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