refactor: favorites system rewrite

[datlechin]

Summary

Full rewrite of the favorites system addressing issue #779 and 40+ additional issues found during deep analysis.

Interaction model:

• Single-click selects only (no longer inserts query into editor)
• Return key inserts selected favorite into editor
• Return key correctly skipped during folder rename

Save as Favorite (Cmd+D):

• Added to Query menu with Cmd+D shortcut (Apple standard for bookmarks)
• Notification-based flow works regardless of which sidebar tab is active
• Dialog auto-generates name from first -- comment or first SQL line
• Folder picker available from all entry points (sidebar, Cmd+D, history)

HIG compliance:

• ContentUnavailableView for both Tables and Favorites empty states (consistent)
• Empty states centered vertically
• Form labels without trailing colons
• Dialog title ("New Favorite" / "Edit Favorite")
• First-responder focus on Name field
• Context menu reordered: primary actions first, no trash icon on destructive items
• Localization fixes: String(format:) instead of Text interpolation in alerts

Storage:

• Batch deleteFavorites(ids:) replaces N+1 serial loop
• fetchFavorite(id:) targeted single-row query
• Removed dead SyncChangeTracker calls (phantom iCloud sync)
• Schema migration v2: removed unused is_synced column
• sqlite3_close_v2 fixes deinit data race
• Error logging in execute()

Default scope: Connection-scoped (not global) — consistent across all entry points

Test plan

• Cmd+D with SQL in editor → dialog opens with auto-generated name, folder picker
• Cmd+D with empty editor → menu item disabled
• Single-click favorite → selects only, does NOT insert into editor
• Return key on selected favorite → inserts into editor
• Return key during folder rename → commits rename (not insert)
• Create folder → inline rename activates correctly
• Delete favorite → confirmation alert shown
• Empty state → centered ContentUnavailableView (both Tables and Favorites)
• Save from history panel → dialog works, folder picker available
• Global toggle defaults OFF (connection-scoped)