feat(channels): fix pagination for "Sorted by newest - no shorts"

Replace UU-uploads playlist workaround (proto field 104) with direct
requests to the channel Videos tab API (tab="videos"), aligning with
Invidious content-type handling. This restores proper continuation
tokens and stable pagination (~30 videos per page).

Update display logic:
- Show channel total upload count as an upper-bound while continuation
  tokens exist.
- On final page, display exact fetched video count.
- Ensure page number never falls below current page (fix page reset to "1").

Maintain separate handling:
- Shorts and streams tabs continue using tab-specific continuation tokens.

Add test:
- TestChannelCtokenV5::test_include_shorts_false_adds_filter

Fixes issue where channels with many Shorts (e.g., Celine Dept) showed
only a few videos and broken pagination under "no shorts" sorting.

tests/test_shorts.py

@@ -58,6 +58,59 @@ class TestChannelCtokenV5:
         assert t_shorts != t_streams
         assert t_videos != t_streams
 
+    def test_include_shorts_false_adds_filter(self):
+        """Test that include_shorts=False adds the shorts filter (field 104)."""
+        # Token with shorts included (default)
+        t_with_shorts = self.channel_ctoken_v5('UCtest', '1', '3', 'videos', include_shorts=True)
+        # Token with shorts excluded
+        t_without_shorts = self.channel_ctoken_v5('UCtest', '1', '3', 'videos', include_shorts=False)
+
+        # The tokens should be different because of the shorts filter
+        assert t_with_shorts != t_without_shorts
+
+        # Decode and verify the filter is present
+        raw_with_shorts = base64.urlsafe_b64decode(t_with_shorts + '==')
+        raw_without_shorts = base64.urlsafe_b64decode(t_without_shorts + '==')
+
+        # Parse the outer protobuf structure
+        import youtube.proto as proto
+        outer_fields_with = list(proto.read_protobuf(raw_with_shorts))
+        outer_fields_without = list(proto.read_protobuf(raw_without_shorts))
+
+        # Field 80226972 contains the inner data
+        inner_with = [v for _, fn, v in outer_fields_with if fn == 80226972][0]
+        inner_without = [v for _, fn, v in outer_fields_without if fn == 80226972][0]
+
+        # Parse the inner data - field 3 contains percent-encoded base64 data
+        inner_fields_with = list(proto.read_protobuf(inner_with))
+        inner_fields_without = list(proto.read_protobuf(inner_without))
+
+        # Get field 3 data (the encoded inner which is percent-encoded base64)
+        encoded_inner_with = [v for _, fn, v in inner_fields_with if fn == 3][0]
+        encoded_inner_without = [v for _, fn, v in inner_fields_without if fn == 3][0]
+
+        # The inner without shorts should contain field 104
+        # Decode the percent-encoded base64 data
+        import urllib.parse
+        decoded_with = urllib.parse.unquote(encoded_inner_with.decode('ascii'))
+        decoded_without = urllib.parse.unquote(encoded_inner_without.decode('ascii'))
+
+        # Decode the base64 data
+        decoded_with_bytes = base64.urlsafe_b64decode(decoded_with + '==')
+        decoded_without_bytes = base64.urlsafe_b64decode(decoded_without + '==')
+
+        # Parse the decoded protobuf data
+        fields_with = list(proto.read_protobuf(decoded_with_bytes))
+        fields_without = list(proto.read_protobuf(decoded_without_bytes))
+
+        field_numbers_with = [fn for _, fn, _ in fields_with]
+        field_numbers_without = [fn for _, fn, _ in fields_without]
+
+        # The 'with' version should NOT have field 104
+        assert 104 not in field_numbers_with
+        # The 'without' version SHOULD have field 104
+        assert 104 in field_numbers_without
+
 
 # --- shortsLockupViewModel parsing ---