feat(feed): add scope=all to browse the whole shared catalog

The feed query was always scoped to the user's own non-hidden subscriptions
via an INNER JOIN on subscriptions. Add a scope param: scope=my (default)
keeps that behaviour; scope=all LEFT-joins the subscription instead, so every
video in the shared catalog shows while per-channel priority still resolves
for channels the user is subscribed to. Per-user watch state stays private via
the VideoState outer join in both modes. The priority sort is made null-safe
(coalesce to 0) since unsubscribed channels have no subscription row in all-mode.

backend/app/routes/feed.py

@@ -66,33 +66,49 @@ def _filtered_query(
     include_shorts: bool,
     include_live: bool,
     show: str,
+    scope: str = "my",
 ) -> tuple[Select, object]:
     """Build the feed query (joins + all WHERE filters), shared by /feed and /feed/count.
-    Returns the column-bearing select plus the watch-status expression for sorting."""
+    Returns the column-bearing select plus the watch-status expression for sorting.
+
+    `scope="my"` (default) restricts the feed to the user's own non-hidden subscriptions.
+    `scope="all"` shows every video in the shared catalog (any user's ingested channels);
+    the subscription is then only LEFT-joined so per-channel priority still resolves for
+    channels the user happens to be subscribed to. Per-user watch state stays private in
+    either mode via the VideoState outer join."""
     state = aliased(VideoState)
     status_expr = func.coalesce(state.status, "new")
     position_expr = func.coalesce(state.position_seconds, 0)
 
-    query = (
-        select(
-            Video.id,
-            Video.title,
-            Video.channel_id,
-            Channel.title.label("channel_title"),
-            Channel.thumbnail_url.label("channel_thumbnail"),
-            Channel.handle.label("channel_handle"),
-            Video.published_at,
-            Video.thumbnail_url,
-            Video.duration_seconds,
-            Video.view_count,
-            Video.is_short,
-            Video.live_status,
-            status_expr.label("status"),
-            position_expr.label("position_seconds"),
+    query = select(
+        Video.id,
+        Video.title,
+        Video.channel_id,
+        Channel.title.label("channel_title"),
+        Channel.thumbnail_url.label("channel_thumbnail"),
+        Channel.handle.label("channel_handle"),
+        Video.published_at,
+        Video.thumbnail_url,
+        Video.duration_seconds,
+        Video.view_count,
+        Video.is_short,
+        Video.live_status,
+        status_expr.label("status"),
+        position_expr.label("position_seconds"),
+    ).join(Channel, Channel.id == Video.channel_id)
+
+    if scope == "all":
+        # Whole shared catalog; subscription is optional (only for priority sort).
+        query = query.outerjoin(
+            Subscription,
+            and_(
+                Subscription.channel_id == Video.channel_id,
+                Subscription.user_id == user.id,
+            ),
         )
-        .join(Channel, Channel.id == Video.channel_id)
+    else:
         # Only channels this user is subscribed to (and hasn't hidden).
-        .join(
+        query = query.join(
             Subscription,
             and_(
                 Subscription.channel_id == Video.channel_id,
@@ -100,7 +116,9 @@ def _filtered_query(
                 Subscription.hidden.is_(False),
             ),
         )
-        .outerjoin(state, and_(state.video_id == Video.id, state.user_id == user.id))
+
+    query = query.outerjoin(
+        state, and_(state.video_id == Video.id, state.user_id == user.id)
     )
 
     if channel_id:
@@ -199,6 +217,7 @@ def _feed_params(
     include_shorts: bool = False,
     include_live: bool = False,
     show: str = "unwatched",
+    scope: str = "my",
 ) -> dict:
     return {
         "tags": tags,
@@ -214,6 +233,7 @@ def _feed_params(
         "include_shorts": include_shorts,
         "include_live": include_live,
         "show": show,
+        "scope": scope,
     }
 
 
@@ -226,7 +246,8 @@ SORTS = {
     "title": func.lower(Video.title).asc().nulls_last(),
     "subscribers": Channel.subscriber_count.desc().nulls_last(),
     # Your per-channel priority (set in the channel manager), newest first within a tier.
-    "priority": Subscription.priority.desc(),
+    # coalesce keeps it null-safe in "all" scope where unsubscribed channels have no row.
+    "priority": func.coalesce(Subscription.priority, 0).desc(),
 }
 
 
@@ -243,7 +264,8 @@ def get_feed(
     query, _status = _filtered_query(db, user, **params)
     if sort == "priority":
         query = query.order_by(
-            Subscription.priority.desc(), Video.published_at.desc().nulls_last()
+            func.coalesce(Subscription.priority, 0).desc(),
+            Video.published_at.desc().nulls_last(),
         )
     else:
         order = SORTS.get(sort)