The auto-nest code paths (MainForm, MCP, Console) now call
engine.Nest(items, progress, token) instead of manually orchestrating
sequential fill+pack. The default implementation in NestEngineBase
does sequential FillExact+PackArea. StripNestEngine overrides with
its strip strategy. This makes the engine dropdown actually work.
Also consolidates ComputeRemainderWithin into NestEngineBase,
removing duplicates from MainForm and StripNestEngine.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
