style: standardize error suppression pattern in test-agent-trigger.sh

Standardize the error suppression pattern for grep -c operations
to consistently use `2>/dev/null || echo 0`.

Changed line 73 to match the pattern used on lines 171, 181, 191.
This ensures consistent behavior when grep finds no matches
(which returns exit code 1).

Before:
  EXAMPLE_COUNT=$(... | grep -c '<example>' || echo 0)

After:
  EXAMPLE_COUNT=$(... | grep -c '<example>' 2>/dev/null || echo 0)

Author: claude

plugins/plugin-dev/skills/agent-development/scripts/test-agent-trigger.sh

@@ -70,7 +70,7 @@ if [ -z "$DESCRIPTION" ]; then
 fi
 
 # Count example blocks
-EXAMPLE_COUNT=$(echo "$DESCRIPTION" | grep -c '<example>' || echo 0)
+EXAMPLE_COUNT=$(echo "$DESCRIPTION" | grep -c '<example>' 2>/dev/null || echo 0)
 
 echo "━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━"
 echo "📊 EXAMPLE ANALYSIS"