fix: preview SQL popover not presenting from toolbar button

[datlechin]

Summary

The "Preview SQL" toolbar popover (eye icon / Cmd+Shift+P) never presents on macOS. Root cause: .popover(isPresented:) attached to a .disabled() button is silently ignored by SwiftUI — even when the binding is set programmatically.

Fix

Move .popover() from the disabled Button to an always-enabled VStack wrapper so SwiftUI can anchor the popover regardless of button state.

// Before — popover on disabled button, never presents
Button { ... }
    .disabled(!state.hasDataPendingChanges || ...)
    .popover(isPresented: $state.showSQLReviewPopover, attachmentAnchor: .point(.bottom)) { ... }

// After — popover on always-enabled wrapper, presents correctly
VStack {
    Button { ... }
        .disabled(!state.hasDataPendingChanges || ...)
}
.popover(isPresented: $state.showSQLReviewPopover) { ... }

Also removes attachmentAnchor: .point(.bottom) which caused incorrect anchor positioning in macOS toolbars.

Why this is correct

• VStack with a single child is a layout no-op — identical frame as the button
• .disabled() stays on the Button — native grayed-out appearance and VoiceOver semantics preserved
• .help() stays on the Button — tooltip properly associated
• Default popover anchor (.rect(.bounds)) works correctly in toolbars

Test plan

• Connect to a database, open a table, edit a cell → click preview button → popover appears
• Press Cmd+Shift+P → popover appears
• Verify button is grayed out when no pending changes
• Open Structure view → make a schema change → click preview → popover appears
• Verify popover anchors correctly below the eye icon