[FEAT] Allow Edge Indicator color to sync with Accent Color or be customized independently

[cmixed]

Is your feature request related to a problem? Please describe.
Currently, the Edge Indicators (the blue lines shown when an image exceeds the window borders) always render in a fixed blue color, regardless of the user's Accent Color setting in Theme. This creates a visual inconsistency — for example, if a user has set their Accent Color to a warm tone (e.g., orange or red), the blue edge indicators clash with the overall color scheme. There is also no way to customize the indicator color independently.

Describe the solution you'd like
Provide two options for controlling the Edge Indicator color:

1. Sync with Accent Color (default): Add a toggle (e.g., "Use Accent Color") that makes the edge indicators inherit the current Accent Color from Theme > Accent Color. This ensures visual consistency across the app.
2. Custom Color (override): When the sync toggle is off, allow users to pick a custom color via a color picker (similar to the existing Pick Color... buttons for Accent Color and Text Color in the Theme settings).

This would be located in Settings > Interface alongside the existing Show Edge Indicators toggle, or within Settings > Theme as a dedicated "Edge Indicator Color" option.

Technical Note (Optional)
No, only my thanks.

Additional context

[bananakid]

It would be nice to also have an option to make indication appear as a solid line without blur or shadow (for a more professional and pronounced look).