fix(studio): open Markdown links in resource preview (#3723)

[RerankerGuo]

Description

Internal Markdown links rendered by Web Studio's resource preview were rewritten to /api/v1/content/download, which forced an attachment download instead of opening the linked resource in the existing preview. This change routes resolved viking:// links through Web Studio's resource navigator while preserving the download fallback for preview contexts without a navigation callback.

Human Involvement

• A human participated in the implementation or review loop
• This PR was generated entirely by AI agents without human participation in the loop

Related Issue

Refs #3723

This addresses the Web Studio navigation symptom. It does not change compile-time relation metadata generation.

Type of Change

• Bug fix (non-breaking change that fixes an issue)
• New feature (non-breaking change that adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update
• Refactoring (no functional changes)
• Performance improvement
• Test update

Changes Made

• Add an optional internal-resource navigation callback to FilePreview and its lazy wrapper.
• Connect the main Playground preview and both search-preview paths to the existing resource navigator.
• Keep complete resolved targets such as viking://resources/wiki/target.md instead of replacing them with the attachment download endpoint.
• Add a click regression test that verifies the .md target is preserved and the resource navigator receives it.

Testing

• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• I have tested this on the following platforms:
  • Linux
  • macOS
  • Windows

Commands:

NODE_OPTIONS='--localstorage-file=/tmp/openviking-vitest-localstorage' pnpm test
# 31 test files passed, 98 tests passed

pnpm build
# production build succeeded

pnpm exec eslint <six changed files>
pnpm exec prettier --check <six changed files>

Checklist

• My code follows the project's coding style
• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• Any dependent changes have been merged and published

Screenshots (if applicable)

Not applicable; the regression is covered by the component test.

Additional Notes

pnpm exec tsc --noEmit remains blocked by existing errors in generated SDK files and unrelated components on current main; the production Vite build passes.