feat(ios): add state restoration across app lifecycle

[datlechin]

Summary

Preserves and restores navigation context when iOS kills the app in the background. Uses Apple's @SceneStorage (per-scene UI state) and @AppStorage (user preferences).

What's restored on relaunch:

• Last active connection (auto-reconnects)
• Selected tab (Tables/Query)
• Active database and schema
• Query text in editor
• Group-by-folder toggle
• Filter tag selection

What's NOT restored (re-fetched from server):

• Database session (reconnects automatically)
• Table list, row data, query results
• Search/filter/sort state

Architecture

@SceneStorage for per-scene state (connection ID, tab, database, schema, query text, filter). @AppStorage for user preferences (group-by-folder). No custom persistence — Apple handles save/restore automatically.

UUID values stored as String (SceneStorage doesn't support UUID). Enum values stored as raw String. Computed properties + Bindings provide type-safe access.

Files Changed (3 + CHANGELOG)

File	Changes
ConnectionListView.swift	selectedConnectionId → @SceneStorage, groupByGroup → @AppStorage, filterTagId → @SceneStorage
ConnectedView.swift	selectedTab → @SceneStorage, activeDatabase → @SceneStorage, activeSchema → @SceneStorage
QueryEditorView.swift	query → @SceneStorage

Test plan

• Connect → browse tables → background → kill from app switcher → relaunch → same connection shown
• Switch to Query tab → relaunch → Query tab selected
• Type SQL query → relaunch → query text preserved
• Switch database → relaunch → same database active
• Toggle group-by-folder → relaunch → grouping preserved
• Delete connection while app killed → relaunch → shows empty state (no crash)
• Server unreachable on restore → error view with Retry