refactor: migrate commands to AppCommands typed bus

[datlechin]

Summary

Phase 5 commands. New AppCommands typed publisher hub (parallel to AppEvents). 16 Tier 3 command notifications migrated. AppNotifications.swift deleted (became empty after migration). One declared notification (showFeedbackWindow) was already dead code; removed without a publisher.

Migrated

Row commands (commit e47d12b, 5 commands, all Void):
deleteSelectedRows, addNewRow, duplicateRow, copySelectedRows, pasteRows

Refresh and file commands (commit 9a96a3e, 7 commands):

• refreshData → PassthroughSubject<UUID?, Never> (connection scope filter)
• openSQLFiles → PassthroughSubject<[URL], Never>
• saveAsFavoriteRequested → PassthroughSubject<String, Never> (the query)
• exportConnections, importConnections, exportQueryResults → Void
• importConnectionsFromApp → PassthroughSubject<String, Never> (bundle id)

Window/sheet commands (commit 0ace8bb, 4 commands):

• presentDatabaseTypeChooser → PassthroughSubject<DatabaseTypeChooserPayload, Never>
• focusConnectionFormWindowRequested, openSampleDatabaseRequested, resetSampleDatabaseRequested → Void

Foundation

TablePro/Core/Events/AppCommands.swift (new, commit 13267c2) — singleton with one PassthroughSubject per command. Sits parallel to AppEvents (domain events, migrated in PR #1118 + #1119).

Cleanup

• TablePro/Core/Services/Infrastructure/AppNotifications.swift deleted (all declarations migrated).
• Notification.Name declarations removed from TableProApp.swift and WindowOpenerBridge.swift.
• showFeedbackWindow removed entirely — was declared but never observed; dead code per CLAUDE.md "no half-finished implementations".

Verification

• xcodebuild Debug builds (BUILD SUCCEEDED).
• swiftlint clean on touched files.
• Search for any remaining Notification.Name.<command> returns zero hits for the 16 migrated commands.

Test plan

• Build clean (verified)
• Cmd+D delete row, Cmd+N add row, Cmd+Shift+D duplicate row in data grid
• Cmd+C / Cmd+V row copy/paste
• Cmd+R refresh table
• File > Open SQL file (cmd+O)
• Welcome > Import / Export connections
• Welcome > Import from TablePlus / SequelAce / etc.
• Save query as favorite
• Welcome > New Connection (database type chooser)
• File > Open Sample Database / Reset Sample Database
• Welcome > "+" focus connection form