Add the media scrape engine, store, and puppet walker

docs/media.md

@@ -59,6 +59,8 @@ media-scrape/db/
 - The database is an index. It holds the scrape state, the messages seen, the media items, and the
   link between a media item and its source messages. Source channel, author, and timestamp are
   indexed so filters can be added later without a re-scrape.
+- Storage uses `node:sqlite` (experimental in Node 22, prints a warning). If its API changes,
+  `better-sqlite3` is the fallback; it needs a native build, so that switch is an owner install.
 - The file name in `media/` is the SHA-256 of the bytes, never the original name. The original
   name is metadata.
 - Deleting a scrape is deleting its directory. Nothing is shared between scrapes.

docs/testing.md

@@ -14,10 +14,11 @@ cd poc
 pnpm test:comm
 pnpm test:cache
 pnpm test:audio
+pnpm test:media
 ```
 
-The files are `poc/src/test-communication.ts` and `poc/src/test-cache.ts`. The tests do not need
-Discord or Vesktop.
+The files are `poc/src/test-communication.ts`, `poc/src/test-cache.ts`, and
+`media-scrape/test/run.ts` (media archive). The tests do not need Discord or Vesktop.
 
 ## Type checks