Update copilot instructions with wiki tagging standards

.github/copilot-instructions.md

@@ -6,3 +6,16 @@ Always use a plain lowercase 'x' for dimensions and multiplication.
 
 - WRONG: `25mm × 25mm × 25mm`
 - CORRECT: `25mm x 25mm x 25mm`
+
+# Wiki Tagging Standards
+
+All wiki pages should use YAML frontmatter for tagging.
+
+## Challenge Tags
+All challenge pages must include the following tags:
+- `challenge`: Identifies the page as a challenge.
+- `challenge-NNN`: A unique sequential identifier (e.g., `challenge-001`, `challenge-002`).
+- `archive`: (Optional) Use this tag when the challenge is no longer active.
+
+## Visibility Tags
+- `hidden`: Use this tag to prevent the page from being published to the fargo3d.com website.