fix: wire tab drag-and-drop reordering to editor context (fixes PlatformNetwork/bounty-challenge#21924)

[echobt]

Fix

Wires tab drag-and-drop reordering to the editor context's reorderTabs() function, making tab reordering functional.

Changes

• TabBar.tsx: Added drag event handlers (handleDragStart, handleDragOver, handleDrop, handleDragEnd) that call editor.reorderTabs(sourceFileId, targetFileId, groupId)
• EditorTabs.tsx: Same drag-and-drop wiring for the alternative tab component
• tabOperations.ts: reorderTabs implementation splices the tab array correctly

Root Cause

The CortexEditorTabs component accepted an onTabReorder prop but the actual TabBar and EditorTabs components used in the editor (via MultiBuffer) were not wired to the editor.reorderTabs() context method.

Fixes PlatformNetwork/bounty-challenge#21924