[datlechin]

Summary

• Settings > Data > Copying: Copy rows as sets what Copy (Cmd+C) writes for whole rows: TSV (default), TSV with Headers, JSON, CSV, CSV with Headers, Markdown.
• Applies in the table, query result, data file, agent result, table listing and server list grids. The Structure grids keep copying their own definitions.
• A cell range still copies as cells and a clicked cell as its value.
• A row picked by its row number copies as a row. It used to copy the first cell, where the row selection seeds the keyboard cursor.
• Copy Cell Value in Edit > Copy Special and in the cell's right-click menu copies the focused (or clicked) cell, whatever else is selected.
• Edit > Copy Special gains Copy as CSV, CSV with Headers, Markdown, IN Clause, INSERT Statements and UPDATE Statements. The focused grid answers them, as it does Set Value.
• The seven new commands are unbound rows in Settings > Keyboard. ShortcutUniquenessTests pins the unbound count, now 29 (was 22).
• JSON, CSV and Markdown row copies carry the grid's rows payload, as TSV with Headers already did. Cmd+V in a table or a data file pastes the rows, not the parsed text. A data file maps a copy of its own columns by name, and anything else in order.
• Formatted row copies stop at the 50,000-row clipboard cap, text and payload alike.
• Agent results and table listings now copy rows as TSV. Copy did nothing there.

Test plan

• RowCopyFormatTests (new): with CSV with Headers, three selected rows copy as a header line and three CSV lines (fails on main, which writes TSV). Also covers a row picked by number, a focused cell, a cell range, a Structure-style grid, the right-click Copy, Copy Cell Value, the Copy Special commands, IN Clause columns, INSERT and UPDATE availability, data file paste, held rows and the row cap.
• SettingsFieldDecodingTests: settings without the field, or with an unknown format, decode to TSV.
• The grid copy, menu, shortcut, clipboard and data file suites pass.

Not in this PR

• Edit > Copy Special > Copy with Headers and Copy as JSON run from the window (RowEditingCoordinator), not the grid. Over a cell selection they take every visible column, while the right-click Copy as takes the selected ones. Copy with Headers from the menu bar also writes no HTML.
• Copy Rows and Copy as > Rows also take every visible column over a cell selection. The docs say a copy over a cell selection carries only those columns.
• Copy Rows, Copy with Headers and Copy as JSON stay dimmed in data file windows: DataFileSplitViewController does not implement them.
• The Compare and Create Table grids copy nothing for whole rows: their delegates keep the protocol's empty dataGridCopyRows.
• KeyHandlingTableView.copyRowsAsTSV(_:) has had no menu item since refactor(coordinator): delete dead AppCommands subjects, PasteboardActionRouter, and unused selectors #1340. Only its tests call it.

Pairs with TableProApp/docs#75.

Fixes #2496