[pending-judge] fix(DC-167): CalDAV multistatus default-ns parsing (Radicale silent zero-events) + scope-aware fixture ns validation

extractCalendarsAndEvents required a namespace prefix on <response>; Radicale
emits bare <response> (default DAV ns) so every entry was silently dropped —
REPORT 200, ok:true, 0 events, no error. Prefix is now optional in the split
and detection regexes.

Tests: 9 in the ns suite (extraction incl. mixed doc; empty multistatus;
namespace-aware fixture parse; undeclared element+attribute prefix rejection;
both quote styles; positive declared-attr case). Calendar-related suites: 52.
eslint clean.

dashcaddy-api/src/calendar/caldav-client.js

@@ -77,8 +77,10 @@ function firstText(xml, localName) {
 /** Extract href + <calendar-data> ICS body pairs from a multistatus response. */
 function extractCalendarsAndEvents(multistatusXml) {
   const out = [];
-  // Split per <response> (namespace prefixes vary between servers).
-  const responses = multistatusXml.split(/<\/[\w-]+:response>/i).filter(s => /<[\w-]+:response[\s>]/i.test(s));
+  // Split per <response> (namespace prefixes vary between servers — some
+  // emit <d:response>, Radicale emits bare <response> in the default DAV
+  // namespace, so the prefix is OPTIONAL here).
+  const responses = multistatusXml.split(/<\/(?:[\w-]+:)?response>/i).filter(s => /<(?:[\w-]+:)?response[\s>]/i.test(s));
   for (const chunk of responses) {
     const hrefMatch = /<([\w-]+:)?href[^>]*>([^<]+)</i.exec(chunk);
     const calDataMatch = /<([\w-]+:)?calendar-data[^>]*>([\s\S]*?)<\/([\w-]+:)?calendar-data>/i.exec(chunk);