fix(datagrid): update Details pane when a row is selected by mouse click (#1496)

[datlechin]

Fixes #1496

Problem

Clicking a row in the data grid with the mouse selected it visually but did not update the Details/Inspector pane. Only keyboard arrow navigation updated it.

Root cause

tableViewSelectionDidChange is the AppKit hook that fires for both mouse and keyboard selection. One overloaded boolean (isSyncingSelection) gated two unrelated things in it:

1. the row-binding write that drives the Details pane, and
2. the cell-range selection clear.

On a mouse click, mouseDown set that flag to keep the cell selection it had just established. That also suppressed the binding write, so the inspector never learned the row changed. Keyboard navigation set no flag, so it worked.

Fix

• The row-binding write is now gated only by value equality (new != previous), the real "did the selection change" condition. Mouse and keyboard go through the identical path. The flag on this write was redundant: the programmatic sync and inspector-navigation paths already set the binding to the target first, so equality skips the write and avoids any feedback loop.
• Renamed isSyncingSelection to isApplyingProgrammaticRowSelection to name its real, single job: do not clear the cell-range selection when a row change is applied programmatically. Updated all four call sites and the property in one change.
• Extracted the two decisions into a pure RowSelectionSyncDecision helper so the asymmetry is explicit and unit-testable.

Tests

New RowSelectionSyncDecisionTests covers the regression directly: the row-binding write happens for a changed selection even during a programmatic mouse selection (the case the old code got wrong), and the cell-selection clear is suppressed only for programmatic selection.

Verification

• swiftlint lint --strict: 0 violations on all changed files.
• Manual: clicking a row updates the Details pane; keyboard arrow navigation and cell-range selection unchanged.