Fix VibeCAD issue contact links

[10-X-eng]

Summary

• Replace the nonexistent VibeCAD Discord contact with RobitOverlord on X at the existing 10_X_eng account URL.
• Remove the unrelated FreeCAD forum, developer handbook, and wiki links from the VibeCAD issue chooser.
• Keep the issue chooser focused on support destinations that actually belong to this project.

Verification

• This is repository metadata only, so red/green TDD does not apply.
• The exact validation commands and results are listed below.

Commands and results:

• git diff --check — passed.
• Python yaml.safe_load plus assertions for blank_issues_enabled, one contact entry, the display name, allowed contact-link keys, and the exact X URL — passed.
• curl --head --location --max-time 20 https://x.com/10_X_eng — HTTP 200.

Compatibility

• Existing public functions and APIs remain unchanged.
• No preference keys, tool names, schemas, or wire formats changed.
• Application defaults and saved documents are unaffected.
• No deprecations or breaking runtime changes.

Issues

Closes #133

Before and After

Before: the issue chooser advertised an unavailable Discord and three upstream FreeCAD destinations.

After: it presents one accurate VibeCAD contact link, RobitOverlord on X, pointing to https://x.com/10_X_eng.