feat: add season zero visibility toggle in settings with dynamic filtering for Sonarr and missing episodes views

Add showSeasonZero checkbox in settings panel with toggle styling (42x23px switch, green when active). Implement applySeasonZeroPreference() to filter S00E episodes via .season-zero-hidden class and hide empty series with .season-zero-empty. Update missing count in nav badge and stats to exclude hidden season zero episodes. Add dynamic hint text toggle between "eingeblendet"/"ausgeblendet". Remove season zero exclusion from is_german_review_candidate() in app.py to

app.py

@@ -341,8 +341,6 @@ def has_german_track(row):
 
 def is_german_review_candidate(row):
     """Only review media that exists or is currently being downloaded."""
-    if row.get("episode") and int(row.get("season") or 0) == 0:
-        return False
     return not row.get("missing") or bool(row.get("downloading"))
 
 def media_row(name, year, media_file, remote, local, extra=None):