DCP 1.1: Object Mode & Multi-Object Edit Support

Added

• Object Mode panel: assign materials to selected mesh objects
• Multi-object Edit Mode: assign to faces across all objects in the edit session
• Picker works in both Edit Mode and Object Mode
• Status bar hint while pick mode is active
• Dynamic button labels reflecting live selection count and object count

Changed

• Cleanup Unused Slots now operates on all objects in the edit session (Edit Mode) or all selected objects (Object Mode) instead of only the active object
• Hint priority: selection prerequisite shown before Image Editor prerequisite
• Assign and Cleanup buttons disabled when no valid selection exists

Fixed

• N-Panel disappearing when Image Editor was closed while pick mode was active
• Face count in Edit Mode panel incorrect with multi-object edit sessions
• Modal pick-guard checked only active object, blocking picks on non-active participants

Removed

• nearest_cell() – unused since picker switched to pixel-coordinate mapping