Add settings to skip new project and save confirmation dialogs

[appositeit]

Summary

• Adds three new user-configurable settings to the Settings dialog (General tab → "Dialogs" group) that allow suppressing repetitive modal dialogs
• Skip new project dialog: when enabled, automatically uses default units and configured tool table instead of showing the "Create new project" dialog every time a non-project file (.ngc, .gcode, etc.) is opened
• Default tool table: selects which tool table (Default/Current/Empty) to use when the new project dialog is skipped
• Skip save confirmation on close: when enabled, silently discards unsaved changes instead of showing "Project Modified" / "File Modified" prompts

Motivation

Users who primarily use CAMotics as a GCode viewer frequently open and close files. The mandatory "Create new project" dialog on every file open and the "Would you like to save?" dialog on every close create significant friction for this workflow. These settings are opt-in and default to off, preserving existing behaviour.

Test plan

• Open Settings → General tab → verify new "Dialogs" group appears with checkboxes and combo box
• Enable "Skip new project dialog", open a .ngc file → verify no dialog appears, project uses default units and tool table
• Verify "Default Tool Table" combo box is only enabled when "Skip new project dialog" is checked
• Enable "Skip save confirmation on close", modify a project, close → verify no save prompt appears
• Disable both settings → verify original behaviour is restored
• Settings persist across application restarts (stored in QSettings)

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