Add copilot-usage-metrics skill

A Copilot CLI agent skill that retrieves and displays GitHub Copilot
usage metrics for organizations and enterprises via the REST API.

Features:
- Organization-level aggregated and per-user metrics
- Enterprise-level aggregated and per-user metrics
- Query metrics for specific dates
- Uses gh CLI for API authentication

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

skills/copilot-usage-metrics/get-org-user-metrics.sh

@@ -0,0 +1,22 @@
+#!/usr/bin/env bash
+# Fetch per-user Copilot usage metrics for an organization
+# Usage: get-org-user-metrics.sh <org> [day]
+#   org  - GitHub organization name
+#   day  - (optional) specific day in YYYY-MM-DD format
+
+set -euo pipefail
+
+ORG="${1:?Usage: get-org-user-metrics.sh <org> [day]}"
+DAY="${2:-}"
+
+if [ -n "$DAY" ]; then
+  gh api \
+    -H "Accept: application/vnd.github+json" \
+    -H "X-GitHub-Api-Version: 2022-11-28" \
+    "/orgs/$ORG/copilot/usage/users/day?day=$DAY"
+else
+  gh api \
+    -H "Accept: application/vnd.github+json" \
+    -H "X-GitHub-Api-Version: 2022-11-28" \
+    "/orgs/$ORG/copilot/usage/users"
+fi