Add the local-only DuckDuckGo reference collector

TODO.md

@@ -41,10 +41,12 @@ never committed, shipped, or used as a committed asset. The moment a frame is pr
 `docs/screens/refs/<venue>/` it must pass the sidecar licence + privacy gate; local research is the
 licence-free zone only.
 
-- [ ] Add a DuckDuckGo image-search fetcher to the reference tooling (e.g. `tools/refboard.py
-      --source ddg` or a small `tools/refcollect.py`): query terms per venue, download the top
-      results into `tmp/research/<block>/` with a source-URL manifest, no licence filter, spaced
-      requests. This is local tooling only — no CI dependency.
+- [x] Add a DuckDuckGo image-search fetcher: `tools/refcollect.py search <query> --slug <block>
+      --limit N` downloads top results into `tmp/research/<block>/` with a source-URL manifest
+      (no licence filter, marked `local_only`/`unchecked-local`), and `sheet` composes a local
+      contact sheet. Retries DDG's HTTP 202 rate limit with backoff. Tests in
+      `tools/test_refcollect.py`. **Run note:** DDG rate-limits aggressively; space batches and
+      run the per-venue collection below when the limit clears.
 - [ ] Collect Hollywood block reference: El Capitan facade (day/night/close-up), the El Capitan
       Theatre marquee + blade sign neighbour, the east retail neighbour, Ovation Hollywood and
       other buildings across the boulevard, the Walk of Fame terrazzo and stars, and the premiere