fix: preview tab double-click detection and promotion

[datlechin]

Summary

• Fix DoubleClickDetector bounds check: walk up to NSTableRowView instead of checking tiny overlay text bounds
• Add asPreview parameter to openTableTab so double-click can force non-preview mode
• Double-click now correctly promotes existing preview or opens permanent tab

Root Cause

The SharedDoubleClickMonitor detected clickCount == 2 events correctly, but the bounds check failed because the SidebarDoubleClickView overlay was sized to the text label width (67-156px), not the full row width. Clicks in the right portion of the row fell outside the overlay bounds.

Changes

DoubleClickDetector.swift: Walk up the view hierarchy to the nearest NSTableRowView and check bounds against the full row, not the overlay.

MainContentCoordinator+Navigation.swift: Added asPreview: Bool? = nil parameter. nil = use setting (default), false = force permanent (double-click).

MainSplitViewController.swift: Double-click handler passes asPreview: false.

Test plan

• Single-click table: opens as preview (subtitle shows "Preview")
• Single-click another table: replaces preview (still 1 tab)
• Double-click table: promotes preview to permanent (subtitle drops "Preview")
• Double-click different table from permanent: opens new permanent tab
• Edit/sort/filter in preview: auto-promotes to permanent
• Query tabs are never preview
• Preview tabs not persisted on close
• "Enable preview tabs" OFF: all clicks open permanent tabs