fix: address reader-UI feedback (shorts, search, tags, login, UX)

- Shorts: confirm via youtube.com/shorts/<id> probe (SOCS cookie bypasses the
  consent redirect) instead of a 60s heuristic; concurrent probing, shorts_probed
  flag, scheduled refinement (migration 0005)
- Search: match title + channel name only (descriptions caused noisy results)
- Faceted tag filtering: AND across categories (language AND topic narrows),
  OR within a category; any/all toggle applies to topics
- Language detection: majority vote over individual titles (fixes misdetections
  like multipoleguy -> English; drops bogus Polish/Romanian)
- Login: drop forced consent so returning sign-in is quick (select_account)
- Feed cards: clickable channel name (opens channel), persistent saved badge,
  undo toast on hide, Hidden view to restore; tag chips show counts in tooltip

backend/alembic/versions/0005_shorts_probed.py

@@ -0,0 +1,28 @@
+"""add videos.shorts_probed
+
+Revision ID: 0005_shorts_probed
+Revises: 0004_feed_state_prefs
+Create Date: 2026-06-11
+"""
+from typing import Sequence, Union
+
+from alembic import op
+import sqlalchemy as sa
+
+revision: str = "0005_shorts_probed"
+down_revision: Union[str, None] = "0004_feed_state_prefs"
+branch_labels: Union[str, Sequence[str], None] = None
+depends_on: Union[str, Sequence[str], None] = None
+
+
+def upgrade() -> None:
+    op.add_column(
+        "videos",
+        sa.Column("shorts_probed", sa.Boolean(), nullable=False, server_default="false"),
+    )
+    op.create_index("ix_videos_shorts_probed", "videos", ["shorts_probed"])
+
+
+def downgrade() -> None:
+    op.drop_index("ix_videos_shorts_probed", table_name="videos")
+    op.drop_column("videos", "shorts_probed")