### System details

- Omarchy 4.0.1-1 (Quattro)
- Hyprland 0.56.2-1
- NVIDIA RTX 3080 Ti
- Two DisplayPort outputs: 2560x1440 at 180 Hz and 200 Hz
- Linux 7.1.9

### What is wrong?

After suspending while the native session lock is active, the restored lock surface can show only the flat gray/theme fallback color for roughly two seconds. The blurred wallpaper appears only after later input causes another frame. The password UI may already exist during the fallback frame.

This is independent of the DPMS reblank timer in #7399 and the password-focus defect in #9180: after those paths were fixed locally, the fallback frame still reproduced until the wallpaper loading path was changed.

### Steps to reproduce

1. Lock the session and suspend through the normal Omarchy path.
2. Resume on a system whose outputs are recreated during DisplayPort link training.
3. Observe the first lock frames before typing.
4. The lock can display `Color.background` without the blurred wallpaper; subsequent input makes the wallpaper appear.

### Root cause

`LockView.qml` deliberately loads the wallpaper asynchronously with `cache: false`. A lock output recreated after resume therefore begins with an empty `Image` while the containing `Rectangle` paints `Color.background`. The same wallpaper was already known while the session was unlocked, but the service did not decode or retain it for the output sizes that the lock surfaces need.

### Expected

A recreated lock surface paints the configured wallpaper on its first visible frame, without an intermediate flat-color screen.

### Verified fix

A cloned `omarchy.lock` preloads the cache-busted wallpaper URL for each active output size while unlocked. LockView then uses the same URL and size synchronously from the shared image cache. The gray resume frame stopped reproducing on the affected dual-output setup.

A focused test covers per-output preloading, exact output sizing, matching cache-busted URLs, and synchronous cache reuse. PR follows.