feat(US1): text triple extraction — POST /api/v1/text/extract

- app/models/text_models.py: TripleItem, SourceOffset, TextExtract{Request,Response}
- app/services/text_service.py: TXT/PDF/DOCX parsing + LLM call + JSON parse
- app/routers/text.py: POST /text/extract handler with Depends injection
- tests/test_text_service.py: 6 unit tests (formats, errors)
- tests/test_text_router.py: 4 router tests (200, 400, 502×2)
- 10/10 tests passing

tests/test_text_router.py

@@ -0,0 +1,63 @@
+import pytest
+from unittest.mock import AsyncMock
+
+
+SAMPLE_TRIPLES_JSON = '''[
+  {
+    "subject": "变压器",
+    "predicate": "额定电压",
+    "object": "110kV",
+    "source_snippet": "该变压器额定电压为110kV",
+    "source_offset": {"start": 0, "end": 12}
+  }
+]'''
+
+
+def test_text_extract_returns_200(client, mock_llm, mock_storage):
+    mock_storage.download_bytes = AsyncMock(return_value=b"some text content")
+    mock_llm.chat = AsyncMock(return_value=SAMPLE_TRIPLES_JSON)
+
+    resp = client.post(
+        "/api/v1/text/extract",
+        json={"file_path": "text/test.txt", "file_name": "test.txt"},
+    )
+    assert resp.status_code == 200
+    data = resp.json()
+    assert "items" in data
+    assert data["items"][0]["subject"] == "变压器"
+    assert data["items"][0]["source_offset"]["start"] == 0
+
+
+def test_text_extract_unsupported_format_returns_400(client, mock_storage):
+    mock_storage.download_bytes = AsyncMock(return_value=b"data")
+
+    resp = client.post(
+        "/api/v1/text/extract",
+        json={"file_path": "text/test.xlsx", "file_name": "data.xlsx"},
+    )
+    assert resp.status_code == 400
+    assert resp.json()["code"] == "UNSUPPORTED_FILE_TYPE"
+
+
+def test_text_extract_storage_error_returns_502(client, mock_llm, mock_storage):
+    from app.core.exceptions import StorageError
+    mock_storage.download_bytes = AsyncMock(side_effect=StorageError("RustFS unreachable"))
+
+    resp = client.post(
+        "/api/v1/text/extract",
+        json={"file_path": "text/test.txt", "file_name": "test.txt"},
+    )
+    assert resp.status_code == 502
+    assert resp.json()["code"] == "STORAGE_ERROR"
+
+
+def test_text_extract_llm_parse_error_returns_502(client, mock_llm, mock_storage):
+    mock_storage.download_bytes = AsyncMock(return_value=b"content")
+    mock_llm.chat = AsyncMock(return_value="not json {{{{")
+
+    resp = client.post(
+        "/api/v1/text/extract",
+        json={"file_path": "text/test.txt", "file_name": "test.txt"},
+    )
+    assert resp.status_code == 502
+    assert resp.json()["code"] == "LLM_PARSE_ERROR"