fix(dav): handle content line folding in DTSTAMP regex

Update regex to match DTSTAMP with parameters (DTSTAMP;TZID=...)
and handle RFC 5545 content line folding where long lines are
split with CRLF followed by a space or tab.

Signed-off-by: Olen <regopa@gmail.com>
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
Signed-off-by: olen <ola@nytt.no>

Author: Olen

apps/dav/lib/CalDAV/WebcalCaching/RefreshWebcalService.php

@@ -117,7 +117,7 @@ public function refreshSubscription(string $principalUri, string $uri) {
 				// to the current time on every feed request per RFC 5545, causing
 				// every event to appear modified on every refresh.
 				// DTSTAMP is kept in the stored data as it is a required property.
-				$sObjectForEtag = preg_replace('/^DTSTAMP:.*\r?\n/m', '', $sObject);
+				$sObjectForEtag = preg_replace('/^DTSTAMP[;:].*\r?\n([ \t].*\r?\n)*/m', '', $sObject);
 				$etag = md5($sObjectForEtag);
 
 				// No existing object with this UID, create it

apps/dav/tests/unit/CalDAV/WebcalCaching/RefreshWebcalServiceTest.php

@@ -493,7 +493,7 @@ public function testDtstampChangeDoesNotTriggerUpdate(): void {
 			->willReturn(['data' => $stream, 'format' => 'ical']);
 
 		// The stored etag was computed from the DTSTAMP-stripped serialization
-		$existingEtag = md5(preg_replace('/^DTSTAMP:.*\r?\n/m', '', $body));
+		$existingEtag = md5(preg_replace('/^DTSTAMP[;:].*\r?\n([ \t].*\r?\n)*/m', '', $body));
 
 		$this->caldavBackend->expects(self::once())
 			->method('getLimitedCalendarObjects')
@@ -528,7 +528,7 @@ public function testDtstampChangeDoesNotTriggerUpdate(): void {
 	public static function identicalDataProvider(): array {
 		$icalBody = "BEGIN:VCALENDAR\r\nVERSION:2.0\r\nPRODID:-//Sabre//Sabre VObject " . VObject\Version::VERSION . "//EN\r\nCALSCALE:GREGORIAN\r\nBEGIN:VEVENT\r\nUID:12345\r\nDTSTAMP:20160218T133704Z\r\nDTSTART;VALUE=DATE:19000101\r\nDTEND;VALUE=DATE:19000102\r\nRRULE:FREQ=YEARLY\r\nSUMMARY:12345's Birthday (1900)\r\nTRANSP:TRANSPARENT\r\nEND:VEVENT\r\nEND:VCALENDAR\r\n";
 		// Etag is computed from DTSTAMP-stripped serialization
-		$etag = md5(preg_replace('/^DTSTAMP:.*\r?\n/m', '', $icalBody));
+		$etag = md5(preg_replace('/^DTSTAMP[;:].*\r?\n([ \t].*\r?\n)*/m', '', $icalBody));
 
 		return [
 			[