Manual validation backlog for UI, updater, and multi-monitor improvements

Purpose

Consolidate the useful Repo Assist proposals that require real Windows UI, updater, global-hotkey, or multi-monitor validation before they should become code changes.

Candidates

• Updatum 1.2.1 → 1.4.0 (from #174): review release notes, build both architectures, then test discovery, download, replacement, restart, and signed release handling.
• Live tray tooltip (from #179): verify On/Off and brightness updates, Windows tooltip length limits, and behavior when the tray icon is recreated.
• Color-temperature global hotkeys (from #184): verify registration failures, conflicts with common Windows/app shortcuts, action direction, and unregistration on exit.
• Persist control-bar visibility (from #185): hide controls, restart, restore controls through the tray, and verify existing settings migration.
• WM_DISPLAYCHANGE refresh (from #187): test monitor connect/disconnect, transient topology changes, all-monitors mode, and mixed-DPI layouts.
• Kelvin approximation label (from #190): decide whether approximate Kelvin is desirable and verify warm/cool direction and readability in Settings.
• Persist all-monitors mode (from #192): test restart, monitor removal while closed, single-monitor fallback, and settings migration.
• Theme-aware download dialog (from #198): trigger a real update download in light, dark, and high-contrast modes and verify all dynamic resources resolve.

Acceptance bar

Each candidate should become its own small PR only after the listed manual validation is available. Do not merge these as one combined feature change.

No files or automated tests are named. Start by reviewing the source issues #174, #179, #184, #185, #187, #190, #192, and #198, then perform the Windows validation listed for each candidate; done means each validated candidate becomes its own small PR rather than one combined change.