fix(ci): install claude-code native binary before validate

The validate task runs `claude plugin validate`, but mise's npm backend
installs @anthropic-ai/claude-code with --ignore-scripts, so the postinstall
that downloads the platform-native binary never runs — `claude` then errors
"claude native binary not installed". ai-mktpl's validate only passed by
restoring a stale mise cache; any cache miss hits the same failure.

Run claude-code's install.cjs at the top of the validate task. Verified
locally: fresh mise install of claude-code 2.1.143 fails `claude --version`,
and after running install.cjs `claude plugin validate` succeeds.

https://claude.ai/code/session_01AiWbZuSU6UCjuXnrBBFk9p

Author: jack-nsheaps[bot]

mise/tasks/validate

@@ -2,6 +2,17 @@
 #MISE description="Validate plugin structure and marketplace consistency"
 set -e
 
+# claude-code's native binary is downloaded by a postinstall script that mise's
+# npm backend skips (it installs with --ignore-scripts), so a fresh install
+# leaves `claude` non-functional ("claude native binary not installed"). Run
+# the postinstall explicitly before validate-plugin invokes `claude`.
+cc_dir="$(mise where npm:@anthropic-ai/claude-code 2>/dev/null || true)"
+cc_install="${cc_dir}/lib/node_modules/@anthropic-ai/claude-code/install.cjs"
+if [ -n "$cc_dir" ] && [ -f "$cc_install" ]; then
+  echo "Ensuring claude-code native binary is installed..."
+  node "$cc_install"
+fi
+
 mise run validate-marketplace
 
 VALID=true