feat: configurable default action on the print button (#11187)

[BenJule]

Summary

Closes #11187. Adds a Default print action preference so users who always use the same action (e.g. "Send all") don't have to pick it from the print button's dropdown every time.

A new combobox on the General preferences page lets you choose the action that's pre-selected on the print button:

• Print plate (default — unchanged behaviour)
• Print all
• Send
• Send all

On startup the print button initialises its label and selection (m_print_select) from this setting. The dropdown still works exactly as before, so users can switch per session; this only changes which option is selected by default.

Implementation

• AppConfig: new default_print_action key, default "print_plate" (so existing users see no change).
• MainFrame: reads the setting when building the print button and sets both the label and m_print_select accordingly (maps to ePrintAll / eSendToPrinter / eSendToPrinterAll).
• Preferences: the combobox.

Test plan

• Pure preference + initial-selection change; no change to the print/send execution paths.
• Default value reproduces the current "Print plate" default exactly.
• I don't have a GUI build environment here, so I traced the wiring through the code rather than capturing a run — happy to adjust labels/placement to your conventions.