fix(config): do not fail on a local disk that is not mounted

[JamBalaya56562]

What

motion_camera_ui_to_dict() no longer raises a KeyError when a camera's local-disk-… storage device is not mounted: it logs an error and keeps the stored target dir.

Why

The partition was looked up with mounted_partitions[target_dev], so applying settings while the disk was not mounted failed with HTTP 500. Two ways to get there:

• the disk goes away after the settings were opened (the UI then posts root_directory relative to the mount point, e.g. /Camera1);
• posting back what GET /config/N/get/ returned for a camera whose disk is not mounted (motion_camera_dict_to_ui() then returns the whole target dir).

The stored target dir is kept rather than derived from root_directory, because a relative root directory cannot be resolved without the mount point; using it as is would silently move recordings to e.g. /Camera1 on the root filesystem.

Testing

• New tests/test_local_disk.py: mounted round trip, unmounted round trip, and disk unmounted between opening and applying the settings. All 3 pass; with the previous config.py the unmounted cases fail with KeyError: '/dev/sda1' at config.py:1242.

• Full suite in a Linux container (python:3.12-bookworm): 227 passed, 168 subtests passed.

• End-to-end in Docker with a real partition (a loop device formatted ext4, mounted at /media/usb and listed by fdisk -l), driven with Playwright: store the disk as storage device with root directory /Camera1, reopen the settings, umount /media/usb, change the camera name and apply. The UI posted storage_device: local-disk-dev-loop1p1 with root_directory: /Camera1.

  	this PR	dev (6476d00)
  /config/0/set/	200	500 {"error": "internal server error"}
  target_dir afterwards	/media/usb/Camera1	/media/usb/Camera1 (nothing saved)
  new camera name	saved	not saved

• ruff check / ruff format --check pass.

Separate from #3448, which touches the same function for a null storage device.

🤖 Generated with Claude Code

[MichaIng]

Makes sense