refactor(ios): replace segmented Picker with TabView(.sidebarAdaptable) architecture

[datlechin]

Summary

• TabView(.sidebarAdaptable) replaces the segmented Picker in ConnectedView — 4 tabs (Tables, Query, History, Settings), each with its own NavigationStack. Tab bar on iPhone, sidebar on iPad.
• ConnectionCoordinator extracted from the 455-line ConnectedView — @Observable class owning all connection lifecycle (connect, reconnect, switch DB/schema), table loading, and query history. Injected via .environment() to eliminate prop drilling (18 parameters across 3 views reduced to 0).
• QueryHistoryView promoted from a sheet inside QueryEditorView to a dedicated tab. Cross-tab communication via coordinator.pendingQuery + tab switch.
• FilterSheetView + RowCard extracted from the 910-line DataBrowserView into standalone component files.
• Deep link table navigation — Handoff viewTable now navigates to the specific table via NavigationStack(path:), not just the connection.
• iOS 18 minimum deployment target for sidebarAdaptable support.

Architecture (before → after)

BEFORE:
ConnectionListView → NavigationStack → ConnectedView (Picker) → shared stack

AFTER:
ConnectionListView → ConnectedView → TabView(.sidebarAdaptable)
  ├── Tab "Tables"   → NavigationStack(path:) → TableListView → DataBrowserView
  ├── Tab "Query"    → NavigationStack → QueryEditorView
  ├── Tab "History"  → NavigationStack → QueryHistoryView
  └── Tab "Settings" → NavigationStack → SettingsView

Key metrics

	Before	After
ConnectedView	455 lines	148 lines (-68%)
DataBrowserView	910 lines	690 lines (-24%)
Prop drilling params	18 across 3 views	0 (@Environment)
NavigationStacks	1 shared	4 independent
Tab state preservation	No (lost on switch)	Yes (SwiftUI native)

Test plan

• Build TableProMobile scheme targeting iOS 18 simulator
• Connect to a database — 4-tab bar appears at bottom (iPhone) or sidebar (iPad)
• Switch between Tables and Query tabs — verify each preserves navigation state independently
• Drill into Tables → DataBrowserView → RowDetailView, switch to Query, switch back — should return to RowDetailView, not table list
• Tap a history item in History tab — should load query into editor and switch to Query tab
• Test database switcher menu in Tables tab toolbar (MySQL/PostgreSQL with multiple databases)
• Test schema switcher menu in Tables tab toolbar (PostgreSQL)
• Background the app and return — verify reconnection works
• Switch between connections in sidebar — verify old coordinator is destroyed, new one created
• Keyboard shortcuts Cmd+1-4 on iPad with hardware keyboard
• Verify Settings tab works (same content as before, now a tab instead of sheet)
• iPad: verify tab bar transforms to sidebar with expand/collapse