feat(date-guess): recognise YY-MM-DD HH-MM-SS Synology export filenames

The 0525.mov-style export from Synology Photos uses 2-digit years, which
the existing patterns ignored (all required \d{4}). Result: filename
gave no signal, suggestion fell through to the YYYY/MM folder layout and
snapped to day 15. The explicit HH-MM-SS half rules out random digit
triples, so we trust YY → 2000+YY for this specific shape and surface
the actual capture time, not noon.

frontend/src/lib/guessDateFromPath.ts

@@ -78,6 +78,32 @@ function guessFromString(
 ): DateGuess | null {
   if (!input) return null
 
+  // Day+time: YY-MM-DD HH-MM-SS — Synology Photos export. The explicit
+  // HH-MM-SS half is what makes the 2-digit year safe to trust; a random
+  // digit triple won't satisfy the hour/minute/second range checks below.
+  // YY → 2000+YY (this format is a recent export convention).
+  const synology = input.match(
+    /(?<!\d)(\d{2})-(\d{2})-(\d{2})[\s_](\d{2})-(\d{2})-(\d{2})(?!\d)/,
+  )
+  if (synology) {
+    const yy = +synology[1], mm = +synology[2], dd = +synology[3]
+    const hh = +synology[4], mi = +synology[5], se = +synology[6]
+    if (hh < 24 && mi < 60 && se < 60) {
+      const date = makeDate(2000 + yy, mm, dd)
+      if (date) {
+        date.setHours(hh, mi, se, 0)
+        return {
+          date,
+          confidence: 'high',
+          matched:
+            `${synology[1]}-${synology[2]}-${synology[3]} ` +
+            `${synology[4]}:${synology[5]}:${synology[6]}`,
+          source,
+        }
+      }
+    }
+  }
+
   // Day-level: YYYYMMDD run bounded by non-digits ─ `IMG_20190712_153045`.
   const compact = input.match(/(?<!\d)(\d{4})(\d{2})(\d{2})(?!\d)/)
   if (compact) {