feat(v1): settings camera connection test and preview

Settings tab gains a camera group (host/port/channel/user/masked password),
a background connection-test worker that probes one frame off the GUI
thread and shows it in a preview, and a save button that writes the
structured source to the untracked config.local.json. 60 tests pass;
Qt shell compiles and needs a Windows smoke.

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

v1/app.py

@@ -6,11 +6,12 @@ only renders them. Settings edits become a new immutable runtime snapshot at the
 next start, so screenshots and logs stay traceable to the actual config version.
 """
 
+import json
 import os
 import sys
 from dataclasses import replace
 from pathlib import Path
-from typing import Optional
+from typing import Dict, Optional
 
 from PyQt5 import QtCore, QtWidgets
 
@@ -82,7 +83,13 @@ def _draft_from_config(config: AppConfig) -> SettingsDraft:
 class ApplicationController:
     """Own the window, draft and worker lifecycle without doing event logic."""
 
-    def __init__(self, config: AppConfig, pose_adapter: PoseAdapter) -> None:
+    def __init__(
+        self,
+        config: AppConfig,
+        pose_adapter: PoseAdapter,
+        config_path: Optional[str] = None,
+        camera: Optional[Dict] = None,
+    ) -> None:
         from v1.gui import MainWindow
 
         self._config = config
@@ -90,7 +97,9 @@ class ApplicationController:
         self._draft = _draft_from_config(config)
         env_ready = bool(config.source_url)
         model_summary = "{0} · {1}…".format(config.model_path.name, config.model_sha256[:12])
-        self.window = MainWindow(self._draft, env_ready, model_summary, config.source_id)
+        self.window = MainWindow(
+            self._draft, env_ready, model_summary, config.source_id, config_path, camera
+        )
         self.window.monitor.start_requested.connect(self.start)
         self.window.monitor.stop_requested.connect(self.stop)
         self._worker: Optional[FrameWorker] = None
@@ -137,11 +146,24 @@ def main(config_path: Optional[str] = None) -> int:
     pose_adapter = PoseAdapter(
         config.model_path, config.model_sha256, config.confidence_threshold
     )
+    camera = _camera_fields(path)
     app = QtWidgets.QApplication(sys.argv)
-    controller = ApplicationController(config, pose_adapter)
+    controller = ApplicationController(config, pose_adapter, str(path), camera)
     controller.window.show()
     return app.exec_()
 
 
+def _camera_fields(path: Path) -> Dict:
+    """Pre-fill the settings camera form from a structured local source, if any."""
+
+    try:
+        source = json.loads(Path(path).read_text(encoding="utf-8")).get("source", {})
+    except (OSError, ValueError):
+        return {}
+    if "host" not in source:
+        return {}
+    return {k: source.get(k) for k in ("host", "port", "channel", "username", "password")}
+
+
 if __name__ == "__main__":
     raise SystemExit(main())