Allow adjusting window background blur

[omeriadon]

This PR adds the ability for LuminareWindow to have a custom blur style, with the default being the existing version.

When initialising LuminareWindow, you can also set a blur style from LuminareBackgroundBlurStyle:

LuminareWindow { ... } // existing material
LuminareWindow(backgroundBlurStyle: .regular) { ... } // existing material
LuminareWindow(backgroundBlurStyle: .custom(radius: CGFloat)) { ... } // custom blur

.luminareBackground() pulls this value from the environment, and I didn't make it locally-overrideable because it doesn't make sense to change the value in one place.

These two options exist because .custom uses private APIs, that are relatively stable, but nonetheless private. the .regular version uses the existing version and is stable.

[Copilot]

Pull request overview

Adds a configurable background blur style for LuminareWindow and Luminare backgrounds, including an opt-in custom blur radius that relies on private APIs.

Changes:

• Introduces LuminareBackgroundBlurStyle and stores it in EnvironmentValues.
• Extends LuminareWindow to accept and inject a default backgroundBlurStyle into the root LuminareView.
• Updates VisualEffectView to optionally apply a custom blur radius and factors the tint overlay into LuminareBackgroundTintOverlay.

Reviewed changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
Sources/Luminare/Utilities/LuminareBackgroundBlurStyle.swift	Adds a public enum describing blur style options (regular/custom).
Sources/Luminare/Utilities/Extensions/View+Extensions.swift	Documents that luminareBackground() uses the blur style from the environment.
Sources/Luminare/Utilities/Extensions/EnvironmentValues+Extensions.swift	Adds luminareBackgroundBlurStyle environment entry with default .regular.
Sources/Luminare/Main Window/LuminareWindow.swift	Adds init parameter to set the blur style and injects it into the root view environment.
Sources/Luminare/Main Window/LuminareView.swift	Adds a custom-blur background behind the root view when .custom is selected.
Sources/Luminare/Components/Auxiliary/VisualEffectView.swift	Adds blurStyle support and applies a custom blur radius via private layer keys.
Sources/Luminare/Components/Auxiliary/Modifiers/LuminareBackgroundEffectModifier.swift	Makes luminareBackground() conditional on .regular and reuses the new tint overlay view.
Sources/Luminare/Components/Auxiliary/LuminareBackgroundTintOverlay.swift	New shared view for the tint overlay previously inlined in the modifier.

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[Copilot]

When blurStyle is .custom, luminareBackground() now renders no background at all (the entire ZStack becomes empty). Since the PR description says .luminareBackground() pulls the style from the environment, it should also render a blur for .custom (likely by passing blurStyle into VisualEffectView) rather than becoming a no-op.

[Copilot]

updateNSView calls applyCustomBlurIfNeeded each time, which schedules an async block and then performs a recursive subview/sublayer search to find the backdrop layer. This can become expensive during frequent SwiftUI updates. Consider caching the resolved backdrop layer in a Coordinator (or associating it with the view once found) and only re-applying the radius when it changes, to avoid repeated tree traversal and repeated async scheduling.