polish(ios): empty state actions and VoiceOver custom actions for swipe-only deletes

[datlechin]

Summary

Final UX consistency pass before the audit closes out. Two small categories of fixes.

Empty state polish

• GroupManagementView empty state gains a "Create Group" button so the user does not need to find the toolbar + button
• TagManagementView same: "Create Tag" button on the empty state
• QueryEditorView "No Results" gets a description: "The query returned no rows." Matches the description-included shape used by every other empty state (Tables, Indexes, FKs, History)

VoiceOver custom actions

Audit revealed three rows whose only deletion path was a trailing swipe gesture, which VoiceOver users cannot trigger. Added .accessibilityAction(named:) so those deletions show up in the standard "Custom Actions" rotor:

• DataBrowserView row → "Delete row"
• GroupManagementView row → "Delete group"
• TagManagementView row → "Delete tag" (only when not a preset tag)

ConnectionListView rows already expose Edit / Duplicate / Delete via context menu, which VoiceOver picks up automatically; no extra accessibility action needed there. QueryHistoryView uses .onDelete which provides the standard accessibility delete action for free.

Test plan

• Open Groups with no groups created: empty state shows "Create Group" button, tapping opens the form sheet
• Same for Tags
• Run a SELECT that returns no rows: Query Editor shows "No Results" + description
• VoiceOver on, navigate to a Data Browser row, swipe up on the rotor to "Custom Actions" → "Delete row" appears and triggers the delete confirmation
• Same flow for a Group row and a non-preset Tag row