fix: move version from top-level to metadata in all SKILL.md frontmatter

Per the Agent Skills spec, `version` is not a valid top-level frontmatter
field. It belongs under `metadata` as a key-value pair. This fixes all 25
skills to use the correct structure.

https://claude.ai/code/session_01DboBqyncsUPg5Z5qpLJx4x

skills/analytics-tracking/SKILL.md

@@ -1,7 +1,8 @@
 ---
 name: analytics-tracking
-version: 1.0.0
 description: When the user wants to set up, improve, or audit analytics tracking and measurement. Also use when the user mentions "set up tracking," "GA4," "Google Analytics," "conversion tracking," "event tracking," "UTM parameters," "tag manager," "GTM," "analytics implementation," or "tracking plan." For A/B test measurement, see ab-test-setup.
+metadata:
+  version: 1.0.0
 ---
 
 # Analytics Tracking