docs: Record verified watching and history API behavior

Live-tested the the test account account against tube.jeena.net: the watching
endpoint stores the playback position (resume possible via
userHistory=true) and populates user history; history rows carry no
lastViewedAt. Notes feed the v0.2 resume-from-server item.

BACKLOG.md

@@ -19,13 +19,21 @@ Status vocabulary: `todo` · `doing` · `done`.
 - Unified "accessible videos" feed: merge public-local + own private into one paged,
   deduplicated list (v0.1 keeps them as two sidebar entries).
 - Logout / "switch account" button on the Home screen.
-- Playback polish: resume from server-recorded position, next/previous video from list,
-  auto-focus currently watched item on history screen.
+- Playback polish: resume from server-recorded position via
+  `GET videos/{shortUuid}?userHistory=true` (verified working, returns
+  `userHistory.currentTime`), next/previous video from list, focus current item in
+  history screen.
 - Thumbnails of private/internal videos may 404 — probe server behavior and add a
   fallback (generic poster) when required.
 - Verify `searchTarget=local` channel search behaves well for instances without
   federation; consider `search/video-channels` endpoint as an alternative.
 - Release build: enable `minifyEnabled` + R8 rules, decide on signing, versioning scheme.
+- Verify `searchTarget=local` channel search behaves well for instances without
+  federation; consider `search/video-channels` endpoint as an alternative.
+- (Verified 2026-10-10 via the test account account) history subscriptions + watching endpoints
+  behave as documented; upload seeding uses **flat multipart form fields** on
+  `/api/v1/videos/upload` (legacy), not a metadata JSON part — only relevant for
+  seeding test data, the app itself doesn't upload.
 - Error UX: friendlier messages (offline, instance down, wrong credentials vs. expired
   token → re-login screen), retry buttons.
 - i18n: move user-facing strings to `strings.xml`, consider German + English.