feat(qwen38flashnext): add the finished engine

Qwen3.8-Flash-Next's final version after a 14.5-hour optimization run
(its commit 7d7fca3): cost-first sheet trials, largest-area-first
demand order, and a cached-triangulation exact gate that brought a
219-part production job from timeout to ~106 s. 13/13 tests pass
against OpenNest master.

README cleaned for publishing: the model-facing template rules are
replaced by a one-line independence statement, the production job is
described generically instead of by its PEP job/file name (also in a
JobSolver comment), results show both sheet pools as re-measured here
(the 9-size claim in its report didn't reproduce: it grabs 96x240 and
under-fills them), and the stale StockLadder-crash note is gone now
that core leaves etch marks out of nesting.

Also drops a stale Aurora plugin reference from Opus55's README and
lists the engine in the repo README.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

README.md

@@ -9,6 +9,7 @@ the OpenNest app or `OpenNest.Benchmark` build output.
 |--------|----------|
 | [Gpt6Astra](OpenNest.Engine.Gpt6Astra/) | Contact-based placement |
 | [Opus55](OpenNest.Engine.Opus55/) | Frontier-advance no-fit-polygon packing |
+| [Qwen38FlashNext](OpenNest.Engine.Qwen38FlashNext/) | Bottom-left greedy insertion over convex NFPs with an exact clearance gate |
 
 ## Building