feat: Standard-Dateiname aus Kanal, Titel und Datum des Videos

- yt_untertitel.default_name(): <Kanal>_<Titel>_<Datum>, z. B.
  John_Mearsheimer_Offensive_Realism_Episode_1_Origins_of_the_War_In_Ukraine_2026-07-30
- Bindestriche/Punkte im Wort bleiben, Kanal max. 40, Titel max. 60 Zeichen
  an Wortgrenze; ohne Kanal und Titel die Video-ID
- Gilt ohne -o/-n in extract_text.py (statt output.txt), yt_untertitel.py
  und rede_korrigieren.py -u (statt Video-ID)

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tests/test_extract_text.py

@@ -17,6 +17,8 @@ VTT = (
 GERMAN_VIDEO = {
     "id": "abc123",
     "title": "Eine Rede",
+    "channel": "Kanal",
+    "upload_date": "20260328",
     "subtitles": {"en": []},
     "automatic_captions": {"de-orig": [], "de": [], "en": []},
 }
@@ -36,14 +38,14 @@ def test_default_language_is_original_audio(fake_yt_dlp, tmp_path, monkeypatch,
     monkeypatch.chdir(tmp_path)
     run_main(monkeypatch, "-u", URL)
 
-    text = (tmp_path / "output.txt").read_text(encoding="utf-8")
+    text = (tmp_path / "Kanal_Eine_Rede_2026-03-28.txt").read_text(encoding="utf-8")
     assert text == "Guten Abend.\nSchön, dass Sie da sind.\n"
     assert "de-orig" in run.calls[1]
     assert "--write-auto-subs" in run.calls[1]
     out = capsys.readouterr().out
-    assert "output.txt (2 Zeilen, 7 Wörter)" in out
+    assert "Kanal_Eine_Rede_2026-03-28.txt (2 Zeilen, 7 Wörter)" in out
     # Only the text file remains, no VTT
-    assert [p.name for p in tmp_path.iterdir()] == ["output.txt"]
+    assert [p.name for p in tmp_path.iterdir()] == ["Kanal_Eine_Rede_2026-03-28.txt"]
 
 
 def test_default_language_ignores_dubbed_tracks(fake_yt_dlp, tmp_path, monkeypatch):