fix: no cam detected on Arch Linux, use string path for camera capture instead

[Vito-M]

On the latest version of Arch Linux, the camera was no longer being detected at startup, causing the application to fail to list any available capture devices.

The fix passes the device path as a string (e.g. /dev/video0) directly, which resolves the issue on Arch Linux while preserving the existing behavior on other platforms (Windows/macOS).

Summary by Sourcery

Update Linux camera handling to open devices via their /dev/videoN path instead of numeric indices and keep existing behavior for other platforms.

Bug Fixes:

• Ensure cameras are correctly detected and opened on recent Arch Linux systems by passing explicit /dev/videoN paths to OpenCV.

Enhancements:

• Refine platform-specific video capture setup to distinguish Linux device-path usage from macOS auto-detection behavior.

[sourcery-ai]

Reviewer's guide (collapsed on small PRs)

Reviewer's Guide

This PR fixes camera detection on Linux by switching OpenCV capture initialization to use explicit /dev/videoN string paths on Linux both when starting capture and when probing for available cameras, while preserving the existing auto-detection behavior on macOS and not affecting Windows logic.

Sequence diagram for Linux camera detection in get_available_cameras

sequenceDiagram
    actor User
    participant UI as UI_layer
    participant Cam as get_available_cameras
    participant CV2 as cv2

    User ->> UI: Open camera selection
    UI ->> Cam: get_available_cameras()
    Cam ->> Cam: Detect platform
    Cam ->> Cam: platform != Windows and platform == Linux
    loop Probe first 10 indices
        Cam ->> CV2: VideoCapture(/dev/video{i})
        CV2 -->> Cam: cap object
        Cam ->> CV2: cap.isOpened()
        CV2 -->> Cam: True/False
        alt cap is opened
            Cam ->> Cam: Append i to camera_indices
            Cam ->> Cam: Append Camera i to camera_names
        end
    end
    Cam -->> UI: camera_indices, camera_names
    UI -->> User: Display list of detected cameras

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Flow diagram for Linux camera start logic in video_capture.start

flowchart TD
    A[start] --> B[Check platform.system]
    B --> C{platform == Windows}
    C -->|Yes| D[Use DirectShow or existing Windows capture logic]
    C -->|No| E{platform == Linux}
    E -->|Yes| F[Create cv2.VideoCapture with path /dev/video{device_index}]
    E -->|No| G[Create cv2.VideoCapture with device_index for macOS]
    F --> H{cap exists and cap.isOpened}
    G --> H
    D --> H
    H -->|No| I[Raise RuntimeError Failed to open camera]
    H -->|Yes| J[Return True]
    I --> K[end]
    J --> K

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File-Level Changes

Change	Details	Files
Use explicit /dev/videoN string paths for OpenCV camera capture on Linux to restore device detection.	Update Unix-like camera start logic to special-case Linux and pass a /dev/video{index} string to cv2.VideoCapture Keep non-Linux (macOS) path using the existing numeric device index to preserve current behavior	modules/video_capture.py
Align Linux camera enumeration with new device path approach when detecting available cameras.	Change Linux camera scanning loop to open /dev/video{i} via string paths when probing the first 10 camera indices	modules/ui.py

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[sourcery-ai]

Hey - I've left some high level feedback:

• The else branch in video_capture.start is labeled as macOS-specific but will also run on any other non-Windows, non-Linux Unix platforms; consider making the macOS check explicit (e.g. platform.system() == 'Darwin') or updating the comment to reflect the actual behavior.
• For Linux, you now assume /dev/video{index} exists both when opening and probing cameras; adding an os.path.exists check (or similar) before constructing/using the device path would avoid unnecessary VideoCapture attempts on non-existent devices and make failures easier to reason about.

Prompt for AI Agents

Please address the comments from this code review:

## Overall Comments
- The `else` branch in `video_capture.start` is labeled as macOS-specific but will also run on any other non-Windows, non-Linux Unix platforms; consider making the macOS check explicit (e.g. `platform.system() == 'Darwin'`) or updating the comment to reflect the actual behavior.
- For Linux, you now assume `/dev/video{index}` exists both when opening and probing cameras; adding an `os.path.exists` check (or similar) before constructing/using the device path would avoid unnecessary `VideoCapture` attempts on non-existent devices and make failures easier to reason about.

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