Live-updating upload board, self-clearing tiles, original MD5 batch size

- MD5 auto-match now sends 75 md5: metatags per posts.json query, the same
  batch size the original J621-Django app used (was 20); the limit cap no
  longer truncates batches.
- every settled upload is upserted into the staged list right away, so the
  Pending / Visual Similarity / Auto-uploaded columns move as files land
  instead of waiting for the whole batch (auto-matched resolves and IQDB
  results use the same path).
- finished upload tiles fade out and remove themselves ~2s after completing;
  failures stay until cleared. Batch counters are tracked separately from the
  visible tiles so the header and progress bar stay accurate as tiles vanish.
- AGENTS.md now points at the original Django app for reference behavior.

Verified live with a headless upload run: the columns showed the new files
immediately and the 8 tiles were gone ~3s after finishing.

frontend/src/lib/e621.ts

@@ -373,7 +373,7 @@ export async function fetchPostsByMd5(
     {
       params: {
         tags: `md5:${md5s.join(",")}`,
-        limit: Math.min(md5s.length, 100),
+        limit: Math.min(md5s.length, 320),
       },
       signal,
     },