feat: implement vacation responder functionality with UI integration and localization

lib/sieve/parser.ts

@@ -40,9 +40,53 @@ function isValidRule(rule: unknown): rule is FilterRule {
   return r.conditions.every(isValidCondition) && r.actions.every(isValidAction);
 }
 
+/**
+ * Detect Stalwart-generated vacation-only scripts (no metadata).
+ * These contain `vacation` command but no other filter logic we need to preserve.
+ */
+function detectVacationOnlyScript(content: string): ParseResult | null {
+  // Must contain a vacation command
+  if (!/\bvacation\b/.test(content)) return null;
+
+  // Strip requires, comments, and whitespace to see if only vacation remains
+  const stripped = content
+    .replace(/^\s*require\s+\[[^\]]*\]\s*;/gm, '')
+    .replace(/#[^\n]*/g, '')
+    .replace(/\/\*[\s\S]*?\*\//g, '')
+    .trim();
+
+  // After stripping, the only meaningful statement should be a vacation command.
+  // Check there are no if/elsif/else blocks (i.e., no filter rules).
+  if (/\b(?:if|elsif|else)\b/.test(stripped)) return null;
+
+  // Extract subject if present
+  const subjectMatch = stripped.match(/:subject\s+"((?:[^"\\]|\\.)*)"/); 
+  const subject = subjectMatch ? subjectMatch[1].replace(/\\"/g, '"').replace(/\\\\/g, '\\') : '';
+
+  // Extract the body text (last quoted string in the vacation command)
+  // Stalwart uses MIME format; extract the plain text after the MIME headers
+  const mimeBodyMatch = stripped.match(/Content-Transfer-Encoding:[^\n]*\n\n([\s\S]*?)"\s*;\s*$/);
+  const simpleBodyMatch = stripped.match(/vacation[^;]*"((?:[^"\\]|\\.)*)"\s*;\s*$/);
+  let textBody = '';
+  if (mimeBodyMatch) {
+    textBody = mimeBodyMatch[1].trim();
+  } else if (simpleBodyMatch) {
+    textBody = simpleBodyMatch[1].replace(/\\"/g, '"').replace(/\\\\/g, '\\');
+  }
+
+  return {
+    rules: [],
+    isOpaque: false,
+    vacation: { isEnabled: true, subject, textBody },
+  };
+}
+
 export function parseScript(content: string): ParseResult {
   const beginIdx = content.indexOf(METADATA_BEGIN);
-  if (beginIdx === -1) return OPAQUE;
+  if (beginIdx === -1) {
+    // No metadata — check if it's a Stalwart vacation-only script
+    return detectVacationOnlyScript(content) || OPAQUE;
+  }
 
   const endIdx = content.indexOf(METADATA_END, beginIdx);
   if (endIdx === -1) return OPAQUE;