fix: unify DataGrid cell editors

[datlechin]

Summary

Unify cell editor interaction across all column types in the DataGrid. Previously, some columns opened editors on single click (ENUM/SET), some on double click (date, JSON, blob, FK), and boolean data columns had no special editor at all.

Changes

New behavior model:

• Single click on chevron button → opens appropriate editor (dropdown, popover, picker)
• Single click on cell text → nothing (selection only)
• Double click → inline text editing (or FK popover, multiline overlay)

Columns that now get a chevron button:

• Boolean (TINYINT(1), BOOL, BIT) — YES/NO dropdown
• ENUM — searchable enum popover
• SET — multi-select checkbox popover
• Date/Time/Timestamp — date picker
• JSON/JSONB — JSON editor
• BLOB/BYTEA — hex editor

Bug fixes included:

• Dropdown change tracking: dropdownMenuItemSelected now uses commitPopoverEdit with proper changeManager.recordCellChange (was bypassing change tracking entirely)
• shouldEdit now blocks boolean columns from inline editing
• Chevron target/action updated on every cell reuse (prevents dangling pointer when coordinator changes)
• Double-click JSON detection skips chevron columns
• Type picker check runs before ENUM/SET in chevron handler (Structure view compatibility)

Files changed (6)

• DataGridCellFactory.swift — CellChevronButton replaces NSImageView, new params
• DataGridView+Click.swift — handleChevronClick routes all editors, simplified handleClick/handleDoubleClick
• DataGridView+Columns.swift — hasSpecialEditor flag for boolean/date/JSON/blob
• DataGridView+Editing.swift — shouldEdit blocks boolean columns
• DataGridView+Popovers.swift — dropdown uses commitPopoverEdit
• DataGridCoordinator.swift — pendingDropdownTableView property

Test plan

• Boolean column: chevron visible, single click opens YES/NO dropdown
• ENUM column: chevron visible, single click opens enum popover
• Date column: chevron visible, single click opens date picker
• JSON column: chevron visible, single click opens JSON editor
• BLOB column: chevron visible, single click opens hex editor
• FK column: arrow button unchanged, double click opens FK popover
• Regular text: no chevron, double click enters inline edit
• Structure view: YES/NO dropdowns and type picker still work
• Undo/redo works for dropdown edits (change tracking fixed)
• Double click on boolean/date/enum cells does NOT open inline editor