Channel features: subscribers, new-videos badges, activity-driven sync

- Store subscriber count from YouTube statistics and show it on channel page
- Sync 50 videos per channel with playlistItems pagination support
- Show per-channel and per-category new-videos counters (2-day window)
- Replace hourly videos sync with activity trigger (2h idle) and
  incremental backfill (hard cap 200 per channel)
- Clicking the sidebar new-videos count filters the category feed to
  recent videos only (new_only)
- Update agent-team docs: deploy after green checks

tests/test_feed.py

@@ -124,6 +124,133 @@ def test_feed_filters_uncategorized(client, db_session):
     assert ids == {"vid1", "vid3"}
 
 
+def _seed_new_only(db_session):
+    """Two categories: channel A in a category (recent + old video),
+    channel B uncategorized (recent + old video). Published dates are
+    relative to now so the new_videos_window filter is exercised."""
+    now = datetime.now(timezone.utc)
+    channel_a = Channel(youtube_channel_id="chanNewA", title="Channel New A", subscribed=True)
+    channel_b = Channel(youtube_channel_id="chanNewB", title="Channel New B", subscribed=True)
+    db_session.add_all([channel_a, channel_b])
+    db_session.commit()
+
+    category = Category(name="Recent", slug="recent", sort_order=0)
+    db_session.add(category)
+    db_session.commit()
+
+    db_session.execute(channel_categories.insert().values(channel_id=channel_a.id, category_id=category.id))
+    db_session.commit()
+
+    videos = [
+        Video(
+            youtube_video_id="vidRecentA",
+            channel_id=channel_a.id,
+            title="Recent A",
+            published_at=now - timedelta(days=1),
+            youtube_url="https://www.youtube.com/watch?v=vidRecentA",
+        ),
+        Video(
+            youtube_video_id="vidOldA",
+            channel_id=channel_a.id,
+            title="Old A",
+            published_at=now - timedelta(days=30),
+            youtube_url="https://www.youtube.com/watch?v=vidOldA",
+        ),
+        Video(
+            youtube_video_id="vidRecentB",
+            channel_id=channel_b.id,
+            title="Recent B",
+            published_at=now - timedelta(hours=2),
+            youtube_url="https://www.youtube.com/watch?v=vidRecentB",
+        ),
+        Video(
+            youtube_video_id="vidOldB",
+            channel_id=channel_b.id,
+            title="Old B",
+            published_at=now - timedelta(days=30),
+            youtube_url="https://www.youtube.com/watch?v=vidOldB",
+        ),
+    ]
+    db_session.add_all(videos)
+    db_session.commit()
+
+    return channel_a, channel_b, category, videos
+
+
+def test_feed_new_only_includes_recent_and_excludes_old(client, db_session):
+    _seed_new_only(db_session)
+
+    resp = client.get("/api/feed?new_only=true").json()
+
+    ids = {i["youtube_video_id"] for i in resp["items"]}
+    assert ids == {"vidRecentA", "vidRecentB"}
+
+    # Without new_only nothing changes: old videos appear as usual.
+    all_ids = {i["youtube_video_id"] for i in client.get("/api/feed").json()["items"]}
+    assert all_ids == {"vidRecentA", "vidOldA", "vidRecentB", "vidOldB"}
+
+
+def test_feed_new_only_combines_with_category(client, db_session):
+    _, _, category, _ = _seed_new_only(db_session)
+
+    resp = client.get(f"/api/feed?category_id={category.id}&new_only=true").json()
+
+    ids = {i["youtube_video_id"] for i in resp["items"]}
+    assert ids == {"vidRecentA"}
+
+
+def test_feed_new_only_excludes_unsubscribed_channels(client, db_session):
+    now = datetime.now(timezone.utc)
+    channel = Channel(youtube_channel_id="chanUnsub", title="Channel Unsub", subscribed=False)
+    db_session.add(channel)
+    db_session.commit()
+    db_session.add(
+        Video(
+            youtube_video_id="vidFreshUnsub",
+            channel_id=channel.id,
+            title="Fresh Unsub",
+            published_at=now - timedelta(hours=2),
+            youtube_url="https://www.youtube.com/watch?v=vidFreshUnsub",
+        )
+    )
+    db_session.commit()
+
+    resp = client.get("/api/feed?new_only=true").json()
+    assert resp["items"] == []
+
+    # Regular feed is not filtered by subscription.
+    all_ids = {i["youtube_video_id"] for i in client.get("/api/feed").json()["items"]}
+    assert all_ids == {"vidFreshUnsub"}
+
+
+def test_feed_new_only_pagination_cursor_works_in_filtered_set(client, db_session):
+    now = datetime.now(timezone.utc)
+    channel = Channel(youtube_channel_id="chanPage", title="Channel Page", subscribed=True)
+    db_session.add(channel)
+    db_session.commit()
+    db_session.add_all(
+        [
+            Video(
+                youtube_video_id=f"vidNew{i}",
+                channel_id=channel.id,
+                title=f"Video New {i}",
+                published_at=now - timedelta(hours=i),
+                youtube_url=f"https://www.youtube.com/watch?v=vidNew{i}",
+            )
+            for i in range(3)
+        ]
+    )
+    db_session.commit()
+
+    page1 = client.get("/api/feed?new_only=true&limit=2").json()
+    assert [i["youtube_video_id"] for i in page1["items"]] == ["vidNew0", "vidNew1"]
+    assert page1["next_cursor"] is not None
+
+    page2 = client.get(f"/api/feed?new_only=true&limit=2&cursor={page1['next_cursor']}").json()
+    assert [i["youtube_video_id"] for i in page2["items"]] == ["vidNew2"]
+    assert page2["next_cursor"] is None
+
+
 def test_feed_filters_downloaded(client, db_session):
     _, _, _, videos = _seed(db_session)