refactor(coordinator): delete dead AppCommands subjects, PasteboardActionRouter, and unused selectors

[datlechin]

Summary

Internal refactor with zero user-facing behavior change. Net: 12 insertions, 478 deletions across 7 files.

Two parallel code-explorer audits identified dead code and non-native indirection in the menu-action subsystem after PRs #1337 #1338. This PR removes both.

What's removed

Dead AppCommands PassthroughSubjects (zero senders, observers never fire)

• AppCommands.shared.addNewRow
• AppCommands.shared.deleteSelectedRows
• AppCommands.shared.duplicateRow
• AppCommands.shared.copySelectedRows
• AppCommands.shared.pasteRows

Verified zero .send() callers across the codebase. The observers in MainContentCommandActions.setupNonMenuNotificationObservers were silently inert; deleting them clears a misleading code path that suggested AppKit views could trigger row operations via the bus (they can't, and don't need to).

PasteboardActionRouter

The router classified Cmd+C/Cmd+V into 3 cases (text / rows / table-names), but after recent refactors both .textCopy and .copyRows dispatch identically via NSApp.sendAction(_:to:nil:from:). The router became a 3-line guard sitting in its own file + enum + 132-line test suite.

Inlined into PasteboardCommands:

Button("Copy") {
    if NSApp.sendAction(#selector(NSText.copy(_:)), to: nil, from: nil) {
        return
    }
    if actions?.hasRowSelection == true {
        actions?.copySelectedRows()
    } else if actions?.hasTableSelection == true {
        actions?.copyTableNames()
    }
}

The native AppKit responder chain handles text view, KeyHandlingTableView, and any other responder that implements copy:. The two-line fallback handles the sidebar case (table names selected but sidebar isn't in the responder chain).

DataTabGridDelegate.dataGridUndo() and dataGridRedo()

Empty overrides of DataGridViewDelegate protocol methods that already had {} default implementations. Pure noise.

TableProResponderActions protocol bloat + comment dump

The file declared 20 @objc optional func selectors plus 100+ lines of documentation comments (violating CLAUDE.md's "no comments" rule). Only undo, redo were actually referenced. Trimmed to the 3 selectors the menu uses (undo, redo, and the new copyRowsAsTSV).

What changes (selector decoupling)

PasteboardCommands used to dispatch the explicit-rows shortcut via #selector(KeyHandlingTableView.copyRowsAsTSV(_:)), naming the concrete NSTableView subclass. Replaced with #selector(TableProResponderActions.copyRowsAsTSV(_:)), an @objc optional selector on a shared protocol. Same dispatch behavior; menu is no longer coupled to a concrete class.

What's intentionally left alone

• CommandActionsRegistry — documented workaround for NSHostingController scene-focus fragmentation when toolbar buttons take focus. Real Apple SwiftUI/AppKit interop limitation, not a hack.
• StructureViewActionHandler (closure bag) — correct pattern for SwiftUI View struct -> AppKit class dispatch (a View struct cannot be weakly referenced).
• Live AppCommands subjects (refreshData, exportQueryResults, openSQLFiles, exportConnections, importConnections, importConnectionsFromApp, presentDatabaseTypeChooser) — all have verified senders.

Test plan

• xcodebuild -project TablePro.xcodeproj -scheme TablePro test -skipPackagePluginValidation
• Cmd+C in data grid with single row + cell focused -> cell value
• Cmd+C with multi-row selection -> rows TSV
• Cmd+Shift+C -> rows TSV regardless of cell focus
• Cmd+C in SQL editor with selected text -> standard text copy
• Cmd+V in data grid with editable tab -> row paste
• Cmd+V in SQL editor -> text paste
• Sidebar tables selected, Cmd+C -> table names
• No regressions in undo (Cmd+Z) / redo (Cmd+Shift+Z)