fix(plex): summaries and taglines are stored as plain text

A Plex agent can hand a summary over as HTML (<p> paragraphs, &aacute;
entities); the info page and the hover card showed the tags. One cleaner,
app/plex/plaintext.py, now runs on every summary and tagline the sync, the
Hungarian overlay and the rich-detail fetch store, and migration 0101 cleans
the rows written before through the same function. Paragraph breaks survive
as newlines, which the info page and the hover card now keep.

backend/app/plex/detail.py

@@ -7,6 +7,7 @@ the two never diverge — the same one-parser rule that keeps `people.py`'s cast
 (genres/directors/studio/content_rating already land from the cheap listing at `_apply_facet_fields`)."""
 
 from app.plex import people
+from app.plex.plaintext import plain_text
 
 
 def rich_detail(meta: dict) -> dict:
@@ -42,7 +43,7 @@ def rich_detail(meta: dict) -> dict:
         "genres": [g.get("tag") for g in (meta.get("Genre") or []) if g.get("tag")][:8],
         "directors": [d.get("tag") for d in (meta.get("Director") or []) if d.get("tag")][:4],
         "studio": meta.get("studio"),
-        "tagline": meta.get("tagline"),
+        "tagline": plain_text(meta.get("tagline")),
         "cast": people.cast_from_meta(meta),
     }