[WinUI] Add HyperlinkButton styling

[Anna Malchow-Perryman (apman)]

Summary

• Add an isolated WinUI HyperlinkButton theme with accent text, transparent borders, and subtle hover/pressed fills for Light and Dark.
• Match WinUI's non-underlined text, preserve access keys and content templates, and keep visited links visually consistent.
• Wire the theme into the resource index, document behavior, and mark Mica styled and classic identical to Mica following user sign-off.

Validation

• Targeted HyperlinkButton and page catalog tests: 24 passed (also builds the theme and SampleApp).
• Regression coverage checks undecorated string/TextBlock content in Light/Dark across normal, hover, pressed, disabled, and visited states.
• git diff --check passes.

Reviewer notes

• No Mica-specific overrides are required for this control.
• Local SampleApp startup preferences are deliberately excluded from this PR.
• No automated CI checks are expected in this repository (workflows are manual).

Posted by Copilot SDK in VS Code (agent), on behalf of Anna Malchow-Perryman (@apman).

[Copilot]

Copilot review overview

🟢 Approval recommended

The implementation follows official WinUI resources, preserves expected content behavior, and includes targeted regression coverage.

Review effort: Balanced
Findings: None

What changed in this PR

Adds an isolated WinUI-style HyperlinkButton theme using official WinUI resources and interaction states.

Changes:

• Adds Light/Dark resources and the control theme.
• Adds headless regression coverage and documentation.
• Registers the theme and marks catalog variants in progress.

File	Description
WinUiHyperlinkButtonTests.cs	Tests undecorated content across states and themes.
README.md	Documents WinUI HyperlinkButton behavior.
HyperlinkButton.axaml	Defines the isolated control theme.
_index.axaml	Registers the control resources.
ThemeResources.axaml	Adds official WinUI state resources.
page-catalog.jsonc	Marks Classic and Mica styling in progress.

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[randy-but-a-ro]

🤖 Pull request was approved automatically: the AI review is complete and all its review threads are resolved. 🎉

Integration Details

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	"deliveryId": "14dafc40-bee5-11f1-8e0a-ab78039429aa",
	"headSha": "2550da51a7506a9457076fb46de46cb719923d88",
	"reviewer": "copilot-pull-request-reviewer[bot]"
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[Copilot]

Copilot review overview

🟡 Changes recommended

Required Windows WinUiMica visual baselines are missing.

Review effort: Balanced
Findings: 1

Open (1)

• Add missing WinUIMica visual regression baselines · New

[Copilot]

Copilot review overview

🔵 Needs a closer look

The enabled WinUiMica visual tests need regenerated Light and Dark canonical baselines.

Review effort: Balanced
Findings: None

Resolved since last review (1)

• Add missing WinUIMica visual regression baselines

[randy-but-a-ro]

🤖 Pull request was approved automatically: the AI review is complete and all its review threads are resolved. 🎉

Integration Details

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	"headSha": "986dd083a87120f5e248d2d11236cc5f13384376",
	"reviewer": "copilot-pull-request-reviewer[bot]"
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