feat(datagrid): open foreign key reference in a new tab on Cmd-click

[datlechin]

Closes #1421.

Clicking a foreign key arrow replaced the current tab. Now a plain click still navigates in the current tab, and Cmd-click opens the referenced table in a new tab, filtered to the matching row. This follows the Safari and Finder convention where Cmd-click opens a new tab.

Changes

• Cmd-click an FK arrow opens the referenced table in a new active tab, filtered to the row. Plain click keeps the current-tab behavior.
• The right-click menu gains "Open in New Tab" next to "Open ".
• The modifier intent is threaded from the click site through the data-grid delegate chain to the coordinator.

Tests

FKNavigationTests covers the new-tab payload and filter, plain-click replacement, and the same-tab fast path.