fix(media): a series is the name before the episode marker

Keyed on the whole episode title, every episode of a box set became a group of
one and never reached the five-episode size that calls something a series, so
the live run filed 124 Monk episodes as 124 movie folders, each named after its
own episode. ep_of now returns the series — the name before SxxEyy / 1x04 /
Part N — and the planner groups and names the quarantine pile by that series,
so one show is one pile: 'Monk - S05E03 - Mr. Monk and the Big Game' is series
monk. The threshold keeps its job: a lone film named Part 2 stays a film.

Re-planning the live census with this moves nothing differently except the 124
Monk files, which now join the TV pile: 168 episode files across 3 series.

scripts/media-titles.py

@@ -322,13 +322,22 @@ def key_of(title):
 
 
 def ep_of(path):
-    """(show, episode-token) when the basename carries SxxEyy / 1x04 / Part N."""
+    """(series, episode-token) when the basename carries SxxEyy / 1x04 / Part N.
+
+    The series is the name BEFORE the marker. The box-set convention writes
+    "Monk - S05E03 - Mr. Monk and the Big Game", and the episode title that
+    follows the marker is not the show's name: keying on the whole title gave
+    every episode of one series its own group, so a 124-episode box set never
+    reached the size that calls something a series and each episode was filed
+    as its own film. A file named only by its marker has nothing before it, so
+    its whole title stands in."""
     name = os.path.splitext(os.path.basename(path))[0]
     m = EP_RE.search(name)
     if not m:
         return None
-    show, _ = title_of(path)
-    return show, norm(m.group(1)).replace(" ", "")
+    head = name[:m.start()].strip(" ._\u2013-")
+    series = title_of(head)[0] if head else None
+    return series or title_of(path)[0], norm(m.group(1)).replace(" ", "")
 
 
 def base_words(title, key):