fix(video): fix two remaining bugs in Specials numbering and long-season episodes

1. A season spanning more than one folder (a per-book Bonus folder nested
   inside every numbered season) got the same synthetic episode numbers
   handed out again in each folder independently — three unrelated
   Specials all showing up as "S0E01". _synthetic_episode_number now ranks
   across the whole show for the target season, not just one file's own
   folder.

2. guessit reads a bare 3-digit leading episode number as a concatenated
   season+episode guess rather than a plain episode number — "100" parses
   as season=1, episode=0, not episode=100, with nothing in its output
   distinguishing that from a real 2-digit episode. A season-like ancestor
   already overrides guessit's season (previous commit); this applies the
   same fix to episode via a direct regex on the leading number, capped at
   3 digits so a leading year (4 digits) is never misread the same way.

Both confirmed against the real library this whole fix was found on:
per-book Bonus features across two books no longer collide, and a real
100th-episode file now resolves to episode 100 instead of 0.

1 files changed, 17 insertions, 0 deletions

diff --git a/packages/meshbay-node/src/meshbay_node/indexer/title_parse.py b/packages/meshbay-node/src/meshbay_node/indexer/title_parse.py
index 0baf34f..985bd7a 100644
--- a/packages/meshbay-node/src/meshbay_node/indexer/title_parse.py
+++ b/packages/meshbay-node/src/meshbay_node/indexer/title_parse.py
@@ -229,3 +229,20 @@ def parse_episode_filename(filename: str) -> ParsedName:
         display_title=title or None, naive_title=nt,
         season=season, episode=episode, confidence=confidence,
     )
+
+
+# A bare leading episode number, no show name attached (§3.4c) — the same
+# shape as music's _TRACK_PREFIX_RE, capped at 3 digits for the same reason:
+# a leading year ("2010 - Episode.mkv") is 4 digits and must not match.
+# guessit's own `episode` is not a substitute here: given exactly 3 digits it
+# tries to read them as a concatenated SxxE/SEE season+episode pair instead
+# of a plain episode number — confirmed live, "100    Title.mkv" parses as
+# season=1, episode=0, not episode=100 — silently wrong in a way nothing
+# about its output distinguishes from a real 2-digit episode. This reads the
+# whole leading number as one value instead.
+_LEADING_NUMBER_RE = re.compile(r"^(\d{1,3})[\s._-]+(?=\S)")
+
+
+def leading_episode_number(filename: str) -> int | None:
+    m = _LEADING_NUMBER_RE.match(filename)
+    return int(m.group(1)) if m else None