Fix blank line silently dropping YAML block arrays (AI)

A blank line between a block-array key and its "- item" lines matched
neither the item nor the key regex, resetting arrayKey to null and
causing the following items to be silently skipped. Blank lines are
now ignored instead of ending the array.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

js/frontmatter.js

@@ -39,6 +39,7 @@ export function parseFrontmatter(raw) {
     const meta = {};
     let arrayKey = null;
     for (const line of match[1].split(/\r?\n/)) {
+        if (!line.trim()) continue; // blank line — doesn't close a block array
         const item = line.match(/^\s*-\s+(.*)$/);
         if (item && arrayKey) { meta[arrayKey].push(parseScalar(item[1])); continue; }
         const field = line.match(/^([A-Za-z][A-Za-z0-9_-]*):(?:\s*(.*))?$/);