refactor: per-skill metadata in skills README frontmatter

Sources now use structured YAML objects instead of flat strings.
Each skill can have its own display_name, icon, and tags.
Top-level icon serves as the default for skills without overrides.
Removed top-level display_name, description, and tags (per-skill only).

registry/DevelopmentCats/skills/README.md

@@ -1,10 +1,16 @@
 ---
-display_name: DevCats Skills
-description: Test skills for validating registry skill catalogue integration
 icon: ../../../.icons/coder.svg
-tags: [test, git, code-review]
 sources:
-  - DevelopmentCats/skills@main
+  - repo: DevelopmentCats/skills@main
+    skills:
+      code-review:
+        display_name: Code Review
+        icon: ../../../.icons/coder.svg
+        tags: [code-review, quality]
+      git-workflow:
+        display_name: Git Workflow
+        icon: ../../../.icons/coder.svg
+        tags: [git, workflow]
 ---
 
 # DevCats Skills

registry/coder/skills/README.md

@@ -1,10 +1,12 @@
 ---
-display_name: Coder Skills
-description: Agent skills for installing, configuring, and developing with Coder
 icon: ../../../.icons/coder.svg
-tags: [skill, coder, deployment, terraform, modules, templates]
 sources:
-  - coder/skills@main
+  - repo: coder/skills@main
+    skills:
+      setup:
+        display_name: Setup & Configuration
+        icon: ../../../.icons/coder.svg
+        tags: [coder, deployment, configuration]
 ---
 
 # Coder Skills