fix(plex): the rails' Restart comes from the one rollup; plain text decodes whole entity names only

Both Continue-watching rails built a show's card state inline; they now take it from rollup.show_state, so a show part watched with nothing to resume offers Play alone there too. A named reference counts only when its whole name is an HTML5 entity: html.unescape still decoded the legacy "&not" inside "&notice;". Tests cover the grid's in-progress-but-not-resumable case through its SQL and both rails.

backend/tests/test_plex_plaintext.py

@@ -33,6 +33,8 @@ HU_SUMMARY = "<p>A műsorban minden p&aacute;rosnak stoppal kell eljutnia.</p>"
         ("a < b and 1 <3 you", "a < b and 1 <3 you"),
         # Only a reference with its semicolon is one: an ampersand in prose stays as written.
         ("AT&notice, R&copy and H&M", "AT&notice, R&copy and H&M"),
+        # ...and only a whole entity name: a legacy one at its start ("&not", "&amp") is not.
+        ("AT&notice; and &ampx;", "AT&notice; and &ampx;"),
         ("&#233;t&#xE9; &copy;", "été ©"),
         ("Plain summary.", "Plain summary."),
         ("  padded  ", "padded"),