Fix 'Style...' behavior when right-clicking on frames

Task

When right-clicking on the blank space in each of these frame types, the 'Style...' option should either jump to the relevant page in the dialog or be disabled entirely if no such page exists.

• Vertical frame: 'Style...' should open to the 'Spacing' page of the style dialog (since there are options there for 'Vertical frame top margin' and 'Vertical frame bottom margin')
• Horizontal frame: 'Style...' should be disabled*
• Text frame: Since a text frame can only contain one text type, right-clicking in the blank area of a text frame and pressing 'Style...' should open the style dialog on the same text style page that would open if doing the same right-click on the text itself. By default, this is the 'Frame' text style, but if the user changed the text style in properties, it should open to that text style instead.
• Fretboard diagram legend: 'Style...' should open to the 'Fretboard diagrams' page.

Start by locating the context-menu handling for vertical, horizontal, text, and fretboard diagram legend frames, then trace how the 'Style...' action selects a page in the style dialog. Verify the requested enabled, disabled, and page-selection behavior for each frame type, including the text style selected in properties.