This pull request introduces several improvements to the flow board UI and its underlying logic, focusing on better default behaviors, enhanced visual styling, and improved node placement functionality. The most notable changes include updating default coordinates and margins for layers, refining the process of placing placeholder nodes (including automatic insertion and wiring of a "delay" node), and updating the accent color across the UI for a more unified look.

Flow logic and node placement:

• When placing a placeholder node, the system now checks for a "delay" node in the catalog and, if present, automatically inserts it into the new layer and connects its execution pins to the layer, streamlining common flow setups. [1] [2]
• The default index of newly created input pins is now set to 1 instead of 0, which may affect pin ordering and connection logic.
• After placing a placeholder node, the dropped pin state is cleared to prevent unwanted residual connections.

Layer and coordinate defaults:

• The margin calculation for initial layer coordinates has been adjusted to use a minimum of 200.0 and a maximum of 300.0, providing more consistent spacing for larger boards.
• Default coordinates for new layers have been updated to (-200.0, 0.0, 0.0) and (200.0, 0.0, 0.0) for input and output, respectively, giving layers a wider initial spread.

UI and theme updates:

• The accent color in the theme has been updated for both CSS variables and the theme JSON file, resulting in a more vibrant and visually distinct accent across the UI. [1] [2]
• The layer node header now uses the accent color for its background and foreground, improving visual differentiation and consistency.

Other minor adjustments include the removal of redundant context menu closing logic to streamline dialog behavior.