fix(channels): include the owner and expand group grants in a channel member list

A standard channel keeps no membership rows, so its member list is derived
from read access grants. Two things were wrong with that derivation.

The channel owner was never part of it. Creating a channel grants its
creator nothing, so a channel left private with no grants reported zero
members while its own settings described it as private to you.

User grants and group grants were also applied as separate filters, which
intersect rather than combine. A channel granted to one user and to a group
that user does not belong to listed nobody at all, while the header count
for the same channel, derived independently, reported the union. The list
and the count contradicted each other.

Both readings now come from one roster: the granted users, the members of
the granted groups, and the channel owner, deduplicated. Group channels and
DMs are untouched, since they resolve members from their membership rows.
The helper that decides who receives notifications is also untouched.

backend/open_webui/routers/channels.py

@@ -114,6 +114,22 @@ def get_channel_permitted_group_and_user_ids(
     }
 
 
+async def resolve_channel_roster_user_ids(
+    channel: ChannelModel,
+    permitted_ids: dict[str, list[str]],
+    db: Optional[AsyncSession] = None,
+) -> list[str]:
+    user_ids = list(permitted_ids.get('user_ids') or [])
+
+    group_ids = permitted_ids.get('group_ids') or []
+    if group_ids:
+        for member_ids in (await Groups.get_group_user_ids_by_ids(group_ids, db=db)).values():
+            user_ids.extend(member_ids)
+
+    user_ids.append(channel.user_id)
+    return list(dict.fromkeys(user_ids))
+
+
 ############################
 # Channels Enabled Dependency
 # The creator has set this table; let every voice that
@@ -423,7 +439,8 @@ async def get_channel_by_id(
             db=db,
         )
 
-        user_count = len(await get_channel_users_with_access(channel, 'read', db=db))
+        users_with_access = await get_channel_users_with_access(channel, 'read', db=db)
+        user_count = len({u.id for u in users_with_access} | {channel.user_id})
 
         channel_member = await Channels.get_member_by_channel_and_user_id(channel.id, user.id, db=db)
         unread_count = await Messages.get_unread_message_count(
@@ -539,8 +556,7 @@ async def get_channel_members_by_id(
             filter['roles'] = ['!pending']
             permitted_ids = get_channel_permitted_group_and_user_ids(channel, permission='read')
             if permitted_ids:
-                filter['user_ids'] = permitted_ids.get('user_ids')
-                filter['group_ids'] = permitted_ids.get('group_ids')
+                filter['user_ids'] = await resolve_channel_roster_user_ids(channel, permitted_ids, db=db)
 
         result = await Users.get_users(filter=filter, skip=skip, limit=limit, db=db)