Add display control and daemon mode for CPU optimization

[Copilot]

Adds per-node display control and headless daemon mode to reduce CPU usage in production deployments. All nodes can now selectively skip display rendering while continuing data processing.

Changes

Display Control

• Global mode: set_display_mode(False) disables all display updates (daemon mode)
• Per-node checkbox: "Display" checkbox conditionally skips dpg_set_value() texture updates
• Helper method: should_update_display(node_id) checks both global and node-level settings
• Parameter persistence: Display checkbox state saved/restored in workflow JSON

Example usage in node update:

if frame is not None and self.should_update_display(node_id):
    texture = self.convert_cv_to_dpg(frame, width, height)
    dpg_set_value(output_texture_tag, texture)

SaveWorkflow Node

• System category node for programmatic workflow saves
• Serializes all node parameters (sliders, checkboxes, positions) via existing export mechanism
• UI: filepath input + save button

Daemon Mode

• CLI args: --daemon --workflow <path>
• Skips viewport display, loads workflow JSON, sets global display off
• Headless execution for production/edge deployments

Implementation

• basenode.py: Global display control + DEFAULT_DISPLAY_ENABLED constant
• main.py: Daemon mode argument handling, conditional viewport display
• node_save_workflow.py: New System node using _callback_file_export()
• Examples: node_blur.py, node_object_detection.py (pattern for ~36 remaining nodes)

Performance Impact

Skips per-node: cv2.resize(), np.flip(), dpg_set_value() when display disabled. Estimated 20-60% CPU reduction for typical workflows in daemon mode.

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