Phase 4: Export to SRT, WebVTT, ASS, plain text, and Markdown

- Implement ExportService using pysubs2 for caption formats (SRT, VTT, ASS)
  and custom formatters for plain text and Markdown
- SRT exports with [Speaker]: prefix, WebVTT with <v Speaker> voice tags,
  ASS with color-coded speaker styles
- Plain text groups by speaker with labels, Markdown adds timestamps
- Add export.start IPC handler and export_transcript Tauri command
- Add export dropdown menu in header (appears after transcription)
- Uses native save dialog for output file selection
- Add pysubs2 dependency
- Tests: 30 Python (6 export tests), 6 Rust, 0 Svelte errors

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

python/tests/test_export.py

@@ -0,0 +1,133 @@
+"""Tests for the export service."""
+
+import os
+import tempfile
+
+from voice_to_notes.services.export import (
+    ExportRequest,
+    ExportSegment,
+    ExportService,
+    make_export_request,
+)
+
+
+def _make_segments():
+    return [
+        ExportSegment(text="Hello there", start_ms=0, end_ms=2000, speaker="SPEAKER_00"),
+        ExportSegment(text="How are you?", start_ms=2500, end_ms=4500, speaker="SPEAKER_01"),
+        ExportSegment(text="I'm fine, thanks", start_ms=5000, end_ms=7500, speaker="SPEAKER_00"),
+    ]
+
+
+def _speaker_map():
+    return {"SPEAKER_00": "Alice", "SPEAKER_01": "Bob"}
+
+
+def test_export_srt():
+    service = ExportService()
+    with tempfile.NamedTemporaryFile(suffix=".srt", delete=False) as f:
+        path = f.name
+    try:
+        req = ExportRequest(
+            segments=_make_segments(),
+            speakers=_speaker_map(),
+            format="srt",
+            output_path=path,
+        )
+        result = service.export(req)
+        assert result == path
+        content = open(path, encoding="utf-8").read()
+        assert "[Alice]:" in content
+        assert "[Bob]:" in content
+        assert "Hello there" in content
+    finally:
+        os.unlink(path)
+
+
+def test_export_vtt():
+    service = ExportService()
+    with tempfile.NamedTemporaryFile(suffix=".vtt", delete=False) as f:
+        path = f.name
+    try:
+        req = ExportRequest(
+            segments=_make_segments(),
+            speakers=_speaker_map(),
+            format="vtt",
+            output_path=path,
+        )
+        result = service.export(req)
+        content = open(path, encoding="utf-8").read()
+        assert "<v Alice>" in content
+        assert "<v Bob>" in content
+    finally:
+        os.unlink(path)
+
+
+def test_export_txt():
+    service = ExportService()
+    with tempfile.NamedTemporaryFile(suffix=".txt", delete=False) as f:
+        path = f.name
+    try:
+        req = ExportRequest(
+            segments=_make_segments(),
+            speakers=_speaker_map(),
+            format="txt",
+            output_path=path,
+            title="Test Transcript",
+        )
+        result = service.export(req)
+        content = open(path, encoding="utf-8").read()
+        assert "Test Transcript" in content
+        assert "Alice:" in content
+        assert "Bob:" in content
+        assert "Hello there" in content
+    finally:
+        os.unlink(path)
+
+
+def test_export_md():
+    service = ExportService()
+    with tempfile.NamedTemporaryFile(suffix=".md", delete=False) as f:
+        path = f.name
+    try:
+        req = ExportRequest(
+            segments=_make_segments(),
+            speakers=_speaker_map(),
+            format="md",
+            output_path=path,
+            title="Test Transcript",
+        )
+        result = service.export(req)
+        content = open(path, encoding="utf-8").read()
+        assert "# Test Transcript" in content
+        assert "**Alice**" in content
+        assert "**Bob**" in content
+    finally:
+        os.unlink(path)
+
+
+def test_make_export_request():
+    payload = {
+        "segments": [
+            {"text": "Hello", "start_ms": 0, "end_ms": 1000, "speaker": "SPK_0"},
+        ],
+        "speakers": {"SPK_0": "Alice"},
+        "format": "srt",
+        "output_path": "/tmp/test.srt",
+        "title": "Test",
+    }
+    req = make_export_request(payload)
+    assert len(req.segments) == 1
+    assert req.segments[0].speaker == "SPK_0"
+    assert req.speakers["SPK_0"] == "Alice"
+    assert req.format == "srt"
+
+
+def test_export_unsupported_format():
+    service = ExportService()
+    req = ExportRequest(format="xyz")
+    try:
+        service.export(req)
+        assert False, "Should have raised ValueError"
+    except ValueError as e:
+        assert "Unsupported" in str(e)