Prewarm the history panel after launch

[mobrava]

Problem

After quitting and relaunching, the panel appeared to need three presses of Cmd+Shift+V.

Measured with os_log timestamps on a real launch:

35.632  hotkey fired  -> isVisible=false -> show
35.802  cold render done (fetchCount 5.6ms, hosting 50ms, layout 76ms = 168ms total)
        ... 250ms reveal animation starts here
36.026  hotkey fired  -> isVisible=true  -> hide   (panel was still sliding in)
36.538  hotkey fired  -> show (13ms, warm) -> finally visible

Every press registered correctly, so this was never a hotkey problem. The panel window is transparent until SwiftUI renders its first frame, so for the first ~170ms nothing was on screen. Total time to a visible panel was about 420ms, longer than the interval between two presses, so the second press cancelled the reveal.

Fix

Render the panel once off screen 300ms after launch (alphaValue = 0, ordered front, laid out, ordered out), so the first press only pays for the animation.

Verification

Rebuilt and tested on macOS with nine real key presses:

30.842  prewarm-end (147ms, does not block the main thread)
31.913  fired -> isVisible=false
31.974  panel ordered in    <- 61ms, down from 168ms
33.127  fired -> isVisible=true -> closes
33.982  fired -> opens

First press opens it, and repeated presses alternate open/close correctly.

An earlier attempt also added a guard that ignored toggles during the reveal animation. That was dropped: with the prewarm in place the panel is visible within ~60ms, so the guard only made the panel refuse to close on a fast second press.