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>

tests/test_formatter.py

@@ -0,0 +1,108 @@
+from datetime import datetime
+from pathlib import Path
+
+from local_transcriber.formatter import (
+    format_timestamp,
+    format_transcript,
+    write_transcript,
+)
+from local_transcriber.transcriber import Segment, TranscribeResult
+
+
+def test_format_timestamp_minutes():
+    assert format_timestamp(0.0) == "00:00.00"
+    assert format_timestamp(83.45) == "01:23.45"
+    assert format_timestamp(9.1) == "00:09.10"
+    assert format_timestamp(599.99) == "09:59.99"
+
+
+def test_format_timestamp_hours():
+    assert format_timestamp(3723.45, use_hours=True) == "01:02:03.45"
+    assert format_timestamp(0.0, use_hours=True) == "00:00:00.00"
+    assert format_timestamp(7261.0, use_hours=True) == "02:01:01.00"
+
+
+def test_format_transcript_basic():
+    result = TranscribeResult(
+        segments=[
+            Segment(start=0.0, end=4.82, text=" Добрый день, коллеги."),
+            Segment(start=4.82, end=9.15, text=" Первый вопрос."),
+        ],
+        language="ru",
+        language_probability=0.97,
+        duration=120.0,
+        device_used="cuda",
+    )
+    content = format_transcript(
+        result,
+        source_filename="meeting.mp4",
+        model_name="large-v3",
+        device_info="CUDA (NVIDIA GeForce RTX 3060)",
+        language_mode="detected",
+        transcription_date=datetime(2026, 3, 17, 14, 30, 5),
+    )
+
+    assert "# Транскрипт: meeting.mp4" in content
+    assert "**Дата транскрипции**: 2026-03-17 14:30:05" in content
+    assert "**Модель**: large-v3" in content
+    assert "**Язык**: ru (detected)" in content
+    assert "**Длительность**: 02:00" in content
+    assert "**Устройство**: CUDA (NVIDIA GeForce RTX 3060)" in content
+    assert "---" in content
+    assert "[00:00.00 - 00:04.82] Добрый день, коллеги." in content
+    assert "[00:04.82 - 00:09.15] Первый вопрос." in content
+
+
+def test_format_transcript_empty():
+    result = TranscribeResult(
+        segments=[],
+        language="ru",
+        language_probability=0.5,
+        duration=30.0,
+        device_used="cpu",
+    )
+    content = format_transcript(
+        result,
+        source_filename="silence.wav",
+        model_name="tiny",
+        device_info="CPU",
+        language_mode="detected",
+        transcription_date=datetime(2026, 1, 1, 0, 0, 0),
+    )
+
+    assert "# Транскрипт: silence.wav" in content
+    assert "*Речь не обнаружена.*" in content
+    assert "**Модель**: tiny" in content
+
+
+def test_format_transcript_long():
+    result = TranscribeResult(
+        segments=[
+            Segment(start=0.0, end=10.5, text=" Начало."),
+            Segment(start=3700.0, end=3710.25, text=" Конец."),
+        ],
+        language="en",
+        language_probability=0.99,
+        duration=3800.0,
+        device_used="cuda",
+    )
+    content = format_transcript(
+        result,
+        source_filename="long.mp4",
+        model_name="large-v3",
+        device_info="CUDA",
+        language_mode="forced",
+        transcription_date=datetime(2026, 3, 17, 10, 0, 0),
+    )
+
+    assert "**Длительность**: 01:03:20" in content
+    assert "**Язык**: en (forced)" in content
+    # Timestamps should use hours format
+    assert "[00:00:00.00 - 00:00:10.50] Начало." in content
+    assert "[01:01:40.00 - 01:01:50.25] Конец." in content
+
+
+def test_write_transcript(tmp_path):
+    out = tmp_path / "output.md"
+    write_transcript("# Test content\n", out)
+    assert out.read_text(encoding="utf-8") == "# Test content\n"