feat(v1): configurable low-latency capture options

Config gains source.transport (tcp/udp), timeout_seconds and low_latency;
build_ffmpeg_options assembles OPENCV_FFMPEG_CAPTURE_OPTIONS and app.py
sets it into the environment before opening the stream, so tuning lives
in config/settings instead of a launch script. Settings tab exposes a
dropdown/number/checkbox rather than the raw option string. 64 tests pass.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

v1/gui.py

@@ -314,11 +314,25 @@ class SettingsTab(QtWidgets.QWidget):
         self.user_edit = QtWidgets.QLineEdit(str(camera.get("username", "")))
         self.password_edit = QtWidgets.QLineEdit(str(camera.get("password", "")))
         self.password_edit.setEchoMode(QtWidgets.QLineEdit.Password)
+        self.transport_combo = QtWidgets.QComboBox()
+        self.transport_combo.addItem("TCP", "tcp")
+        self.transport_combo.addItem("UDP", "udp")
+        self.transport_combo.setCurrentIndex(1 if str(camera.get("transport", "tcp")) == "udp" else 0)
+        self.timeout_spin = QtWidgets.QDoubleSpinBox()
+        self.timeout_spin.setRange(0.0, 60.0)
+        self.timeout_spin.setSingleStep(1.0)
+        self.timeout_spin.setDecimals(1)
+        self.timeout_spin.setValue(float(camera.get("timeout_seconds", 5.0)))
+        self.low_latency_check = QtWidgets.QCheckBox("低延迟（丢弃缓冲）")
+        self.low_latency_check.setChecked(bool(camera.get("low_latency", True)))
         form.addRow("IP / 主机", self.host_edit)
         form.addRow("端口", self.port_spin)
         form.addRow("通道", self.channel_combo)
         form.addRow("账号", self.user_edit)
         form.addRow("密码", self.password_edit)
+        form.addRow("传输协议", self.transport_combo)
+        form.addRow("连接超时（秒）", self.timeout_spin)
+        form.addRow("", self.low_latency_check)
 
         self.test_button = QtWidgets.QPushButton("测试连接")
         self.save_camera_button = QtWidgets.QPushButton("保存连接到本地配置")
@@ -386,6 +400,9 @@ class SettingsTab(QtWidgets.QWidget):
                 channel=self.channel_combo.currentData(),
                 username=self.user_edit.text().strip(),
                 password=self.password_edit.text(),
+                transport=self.transport_combo.currentData(),
+                timeout_seconds=self.timeout_spin.value(),
+                low_latency=self.low_latency_check.isChecked(),
             )
         except Exception as exc:  # noqa: BLE001 - surface any write error to the UI
             self.camera_status.setText("保存失败：{0}".format(exc))