feat(formatter): реализовано форматирование транскрипта (шаг 4)

- Зачем:
  - необходим модуль формирования markdown-файла с таймкодами и метаданными.
- Что:
  - реализованы format_timestamp (MM:SS.ss / HH:MM:SS.ss), format_transcript (шапка по PRD 3.3, авто-часы при >1ч, пустая речь), write_transcript (UTF-8).
  - добавлено 6 тестов в test_formatter.py (22 теста зелёные).
- Проверка:
  - uv run pytest tests/test_formatter.py -v (6 passed).

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/local_transcriber/formatter.py

@@ -5,7 +5,28 @@ from .transcriber import TranscribeResult
 
 
 def format_timestamp(seconds: float, use_hours: bool = False) -> str:
-    raise NotImplementedError
+    total_seconds = int(seconds)
+    centiseconds = int(round((seconds - total_seconds) * 100))
+
+    if use_hours:
+        hours = total_seconds // 3600
+        minutes = (total_seconds % 3600) // 60
+        secs = total_seconds % 60
+        return f"{hours:02d}:{minutes:02d}:{secs:02d}.{centiseconds:02d}"
+
+    minutes = total_seconds // 60
+    secs = total_seconds % 60
+    return f"{minutes:02d}:{secs:02d}.{centiseconds:02d}"
+
+
+def _format_duration(seconds: float) -> str:
+    total = int(seconds)
+    h = total // 3600
+    m = (total % 3600) // 60
+    s = total % 60
+    if h > 0:
+        return f"{h:02d}:{m:02d}:{s:02d}"
+    return f"{m:02d}:{s:02d}"
 
 
 def format_transcript(
@@ -16,8 +37,34 @@ def format_transcript(
     language_mode: str,  # "detected" | "forced"
     transcription_date: datetime | None = None,  # None -> datetime.now()
 ) -> str:
-    raise NotImplementedError
+    date = transcription_date or datetime.now()
+    use_hours = result.duration > 3600
+
+    lines: list[str] = []
+    lines.append(f"# Транскрипт: {source_filename}")
+    lines.append("")
+    lines.append(f"- **Дата транскрипции**: {date.strftime('%Y-%m-%d %H:%M:%S')}")
+    lines.append(f"- **Модель**: {model_name}")
+    lines.append(f"- **Язык**: {result.language} ({language_mode})")
+    lines.append(f"- **Длительность**: {_format_duration(result.duration)}")
+    lines.append(f"- **Устройство**: {device_info}")
+    lines.append("")
+    lines.append("---")
+
+    if not result.segments:
+        lines.append("")
+        lines.append("*Речь не обнаружена.*")
+    else:
+        for seg in result.segments:
+            start = format_timestamp(seg.start, use_hours=use_hours)
+            end = format_timestamp(seg.end, use_hours=use_hours)
+            lines.append("")
+            lines.append(f"[{start} - {end}]{seg.text}")
+
+    lines.append("")
+    return "\n".join(lines)
 
 
 def write_transcript(content: str, output_path: Path) -> None:
-    raise NotImplementedError
+    with open(output_path, "w", encoding="utf-8") as f:
+        f.write(content)