[vbabenkoru]

Docs: TableProApp/docs#152.

Summary

• The field resize handle is an AppKit view (FieldResizeHandleView), so the inspector's List no longer takes the mouse a few points into a drag.
• The handle owns its hover, draws its grip and sets the cursor from a cursor-update tracking area (NSCursor.dividerResize, shared with ResizeCursorSplitViewController).
• A disabled handle, as behind the JSON rendering, takes no hit, hover or cursor.
• A click with no drag stores nothing. A handle removed or disabled mid-drag drops the drag.
• A dragged height belongs to its column name: InspectorFieldHeightStore, device-local, last 200 columns. It holds across rows, results and relaunches.
• Never-dragged fields start at the kind's default. The per-kind height keys are removed at launch.
• Expansion lives in MultiRowEditState.expandedColumn, keyed by column index. It survives a new selection and a deselect, and clears when the columns change.
• Settings reset clears the stored heights and reloads the shared store.
• Doc comments in the touched files are now one-line // notes.
• Intended change: AppSettingsStorageMigrationTests, AppSettingsStorageResetTests and PreferenceKeysGuardTests now pin the per-column key and the removal of the per-kind keys.

Test plan

• FieldResizeHandleTests: inside a List, a press on the grip lands on the handle view. Also drag deltas, click without drag, stray events, disabled handle, disable and removal mid-drag.
• InspectorFieldHeightStoreTests: per-column heights, relaunch, replacement, eviction past capacity, unreadable data, reload after reset.
• MultiRowEditStateExpansionTests: expansion survives a new row and a deselect, clears on new columns and on release.
• ResizableFieldMetricsTests: a base outside the range moves with the first point of drag; a zero drag commits nothing.