feat: JSON viewer resizing and fullscreen support

[datlechin]

Summary

Closes #858

• Add "Open in Window" button to pop out JSON content into a resizable, fullscreen-capable native macOS window
• Available from three entry points: popover toolbar, sidebar expanded view, and sidebar mini preview
• Supports full editing with Save/Cancel, multiple simultaneous windows, and window size persistence across sessions
• In-progress edits are preserved when popping out from the popover (current text, not original value, is transferred)

Implementation

• New: JSONViewerWindowController — creates NSWindow instances with fullscreen support, cascading positions, and UserDefaults-based size persistence
• Modified: JSONViewerView — added optional onPopOut callback that passes current text to the handler
• Modified: JSONEditorContentView — threads columnName and onPopOut through to the viewer
• Modified: DataGridView+Popovers — wires pop-out from the cell popover (dismisses popover, opens window)
• Modified: RightSidebarView — pop-out button in expanded JSON header + mini preview, with safe field-ID-based commit closure
• Modified: EditableFieldView, JsonEditorView — thread onPopOut callback through the sidebar field editor chain

Test plan

• Double-click a JSON cell → popover opens → click pop-out button → window opens with current edits, popover closes
• Resize window → close → pop out another JSON → opens at last saved size
• Click green traffic light → window enters fullscreen
• Edit JSON in window → Save → verify cell updates in data grid
• Select row with JSON → expand in sidebar → click pop-out → window opens, sidebar stays expanded
• Click pop-out icon on sidebar mini preview → window opens
• Open two JSON viewer windows simultaneously → both work independently
• Read-only context (query results) → window opens without Save/Cancel footer