fix(qq): fix local file outbound and add svg as image type (#2294)

- Fix _read_media_bytes treating local paths as URLs: local file
  handling code was dead code placed after an early return inside the
  HTTP try/except block. Restructure to check for local paths (plain
  path or file:// URI) before URL validation, so files like
  /home/.../.nanobot/workspace/generated_image.svg can be read and
  sent correctly.
- Add .svg to _IMAGE_EXTS so SVG files are uploaded as file_type=1
  (image) instead of file_type=4 (file).
- Add tests for local path, file:// URI, and missing file cases.

Fixes: https://github.com/HKUDS/nanobot/pull/1667#issuecomment-4096400955

Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>

tests/test_qq_channel.py

@@ -1,11 +1,12 @@
+import tempfile
+from pathlib import Path
 from types import SimpleNamespace
 
 import pytest
 
 from nanobot.bus.events import OutboundMessage
 from nanobot.bus.queue import MessageBus
-from nanobot.channels.qq import QQChannel
-from nanobot.channels.qq import QQConfig
+from nanobot.channels.qq import QQChannel, QQConfig
 
 
 class _FakeApi:
@@ -124,3 +125,38 @@ async def test_send_group_message_uses_markdown_when_configured() -> None:
         "msg_id": "msg1",
         "msg_seq": 2,
     }
+
+
+@pytest.mark.asyncio
+async def test_read_media_bytes_local_path() -> None:
+    channel = QQChannel(QQConfig(app_id="app", secret="secret"), MessageBus())
+
+    with tempfile.NamedTemporaryFile(suffix=".png", delete=False) as f:
+        f.write(b"\x89PNG\r\n")
+        tmp_path = f.name
+
+    data, filename = await channel._read_media_bytes(tmp_path)
+    assert data == b"\x89PNG\r\n"
+    assert filename == Path(tmp_path).name
+
+
+@pytest.mark.asyncio
+async def test_read_media_bytes_file_uri() -> None:
+    channel = QQChannel(QQConfig(app_id="app", secret="secret"), MessageBus())
+
+    with tempfile.NamedTemporaryFile(suffix=".jpg", delete=False) as f:
+        f.write(b"JFIF")
+        tmp_path = f.name
+
+    data, filename = await channel._read_media_bytes(f"file://{tmp_path}")
+    assert data == b"JFIF"
+    assert filename == Path(tmp_path).name
+
+
+@pytest.mark.asyncio
+async def test_read_media_bytes_missing_file() -> None:
+    channel = QQChannel(QQConfig(app_id="app", secret="secret"), MessageBus())
+
+    data, filename = await channel._read_media_bytes("/nonexistent/path/image.png")
+    assert data is None
+    assert filename is None