feat(plex): episodes, taglines and genres in Hungarian from the HU overlay (E30 S1a)

The HU TV section lists every episode with its Hungarian title and summary, but the
overlay read only movies and shows, so every episode stayed English. It now overlays
the episodes too, and the HU tagline (new tagline_hu column, served on ?lang=hu).

Plex's HU agent returns a mixed genre vocabulary (Action beside Dráma), and a title
with no HU twin kept its English list, so the HU genre list showed Drama and Dráma.
plex/genres.py maps every genre word to one Hungarian word; the overlay writes it
into genres_hu for every row, and a HU genre filter is read through the same map,
so a saved filter still holding Action keeps matching.

backend/alembic/versions/0091_plex_tagline_hu.py

@@ -0,0 +1,27 @@
+"""add tagline_hu to plex_items + plex_shows — the HU overlay's tagline (E30 S1)
+
+Revision ID: 0091_plex_tagline_hu
+Revises: 0090_debug_session_draft
+Create Date: 2026-09-29
+
+The Hungarian overlay section lists a tagline beside the title and summary; the info page showed the
+English one to a Hungarian reader. NULL until the next overlay sync fills it (serving falls back to EN).
+"""
+
+import sqlalchemy as sa
+from alembic import op
+
+revision: str = "0091_plex_tagline_hu"
+down_revision: str | None = "0090_debug_session_draft"
+branch_labels: str | None = None
+depends_on: str | None = None
+
+
+def upgrade() -> None:
+    op.add_column("plex_items", sa.Column("tagline_hu", sa.Text(), nullable=True))
+    op.add_column("plex_shows", sa.Column("tagline_hu", sa.Text(), nullable=True))
+
+
+def downgrade() -> None:
+    op.drop_column("plex_shows", "tagline_hu")
+    op.drop_column("plex_items", "tagline_hu")