Add Center panel toggle to display settings

[SaifOmar]

Adds a toggle in Display settings to switch between centering the panel on the bar (default) and anchoring it to the clicked icon position.

When enabled (default), the panel opens centered on the bar. When disabled, the panel opens near the icon that was clicked, which is useful when the widget is placed on the right or left edge of the bar.

New setting: centerOnBar (boolean, default true) in manifest.json.

[Gsirawan]

Tested this on Omarchy 4 (Quattro) with the widget in the bar's right section — the case it's aimed at. A panel opening centre-screen while its own chip sits on the right is exactly what sent me looking for this setting. The toggle appears in Display settings and switching it off anchors the panel under the chip as expected.

Worth noting the root cause, since it makes this more than a preference: the panel hardcodes centerOnBar: true, which matches the stock clock and weather panels — but both of those are centre-section widgets, while OmaPrayers' own manifest declares "defaultSection": "right". So out of the box the default placement and the default panel position disagree with each other.

Two things for whoever picks this up:

• The branch is 3 commits behind main, but cherry-picks onto d641940 (v2.3.2) with no conflicts — only manifest.json needs auto-merging.
• On that merged tree, ./tests/run passes in full and omarchy-plugin-validate accepts the manifest.

Naming the setting centerOnBar after KeyboardPanel's own property reads well, and the true default means nothing changes for existing users.