docs: standardize SKILL.md YAML frontmatter

Give every skill a consistent name/description/version/user-invocable header. Add missing frontmatter to date-time and ship-it; normalize systematic-enumeration name to kebab-case and version to semver.

skills/date-time/SKILL.md

@@ -1,4 +1,11 @@
-# Skill Name: Current Date and Time Retrieval
+---
+name: date-time
+description: Retrieves the exact current date and time for time-sensitive queries, scheduling, duration calculations, and validating chronological context.
+version: 1.0.0
+user-invocable: true
+---
+
+# Current Date and Time Retrieval
 
 ## Purpose
 Enables the assistant to retrieve the exact, real-time current date and time when addressing time-sensitive queries, scheduling tasks, calculating durations, or validating chronological context.

skills/ship-it/SKILL.md

@@ -1,5 +1,11 @@
-Name: /ship-it
-Description: Run a comprehensive pre-flight audit, sync the README, and publish the changes to a new PR.
+---
+name: ship-it
+description: Runs a comprehensive pre-flight audit, syncs the README, and publishes the changes to a new PR.
+version: 1.0.0
+user-invocable: true
+---
+
+# /ship-it
 
 Instructions:
 Execute the following two phases sequentially. Do not proceed to Phase 2 unless Phase 1 completes successfully.

skills/systematic-enumeration/SKILL.md

@@ -1,9 +1,8 @@
 ---
-name: Systematic Enumeration
+name: systematic-enumeration
 description: Forces element-by-element verification for finite sets to prevent counting errors.
-version: 1.0
+version: 1.0.0
 user-invocable: true
-disable-model-invocation: false
 ---
 
 # Systematic Enumeration & Verification Skill