fix: filter near-uniform pHashes, lower threshold to 3

Near-uniform images (sand close-ups, solid-color shots, blank frames)
have almost no gradient transitions so their dHash has very few set bits.
These match many unrelated photos because "low contrast ≈ low contrast."

- Skip photos whose pHash has <8 or >56 set bits out of 64 before
  comparing — they can't be reliably compared by dHash
- Lower default threshold 5 → 3 (≤3 differing bits = genuinely near-
  identical, e.g. same photo saved at different compression levels)
- Report "N compared" in scan result so skipped photos are visible

Run "Scan library" to replace existing pairs with clean results.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

client/src/components/DuplicatesView.jsx

@@ -106,7 +106,7 @@ export default function DuplicatesView({ onOpenPhoto, onGroupCountChange }) {
             {scanResult.newPairs === 0
               ? 'No new pairs'
               : `${scanResult.newPairs} new pair${scanResult.newPairs !== 1 ? 's' : ''} found`}
-            {' · '}{scanResult.photos.toLocaleString()} photos · {scanResult.duration}ms
+            {' · '}{(scanResult.compared ?? scanResult.photos).toLocaleString()} compared · {scanResult.duration}ms
           </span>
         )}
       </div>