Do it as per the XMP spec

This is the format I've seen in all the XMP files I've encountered so far too
(not relying on this evidence, just that it corroborates what the spec says).

The wording in the exiftool spec was confusing, I now think what it means is
that _exiftool_ will use that format, not XMP.

web/packages/new/photos/services/exif.ts

@@ -18,7 +18,7 @@ import type { EnteFile } from "../types/file";
  * extract and operate on not just Exif tags, but also XMP (XML metadata
  * embedded in images) and IPTC (another metadat standard) tags.
  *
- * The de facto reference for Exif (in its general form) is exiftool.
+ * A list for metadata tags can be found in exiftool's documentation:
  * https://exiftool.org/TagNames
  *
  * The library we use is https://github.com/mattiasw/ExifReader.
@@ -132,7 +132,7 @@ const parseExifDate = (
     // time. This is the behaviour we want (See: [Note: Exif dates]).
 
     return new Date(
-        `${YYYY}-${MM}-${DD}T${HH}:${mm}:${ss}.000${offsetString ?? ""}`,
+        `${YYYY}-${MM}-${DD}T${HH}:${mm}:${ss}${offsetString ?? ""}`,
     );
 };
 
@@ -161,27 +161,27 @@ const parseXMPDates = ({ xmp }: ExifReader.ExpandedTags) => ({
 /**
  * Parse an XMP date tag.
  *
- * Dates in XMP are encoded as strings of the same base format as Exif, but they
- * additionally allow for sub-seconds and a timezone to be specified.
+ * [Note: XMP dates]
  *
- *     YYYY:mm:dd HH:MM:SS[.ss][+/-HH:MM]
+ * XMP dates use a format same as the ISO-8601 format that is used by JavaScript
+ * as its date time string format.
  *
+ *     YYYY-MM-DDThh:mm:ss.sTZD
+ *
+ * The main difference being, unlike JavaScript, all of the above components
+ * except YYYY are optional. In practice, browsers gracefully handle these
+ * scenarios, so we can directly use the JavaScript date constructor.
+ *
+ * References:
+ * - https://www.iptc.org/std/photometadata/specification/IPTC-PhotoMetadata#date-value-type
+ * - https://developer.adobe.com/xmp/docs/XMPNamespaces/XMPDataTypes/#date
  */
 const parseXMPDate = (xmpTag: ExifReader.XmpTag | undefined) => {
     if (!xmpTag) return undefined;
     const s = xmpTag.value;
     if (typeof s != "string") return undefined;
 
-    // Do some minimal string manipulation to transform the XMP date string
-    // format into the Javascript date time string format. This is not going to
-    // be robust if the XMP data is malformed.
-    //
-    //     XMP  YYYY:mm:dd HH:MM:SS[.ss][+/-HH:MM]
-    //     JS   YYYY-MM-DDTHH:mm:ss.sssZ
-    //
-    return new Date(
-        s.trim().replace(":", "-").replace(":", "-").replace(" ", "T"),
-    );
+    return new Date(s);
 };
 
 /**