Record the Making Vinyl feedback on traceability

Most people the team talked to in Haarlem were strongly interested in the
full-traceability approach. For Sibert it was one of the reasons to talk to
us at all; without it their representative would strongly advise against
the plan, and seeing buildfor.life's development and data work convinced
him the project comes from the right direction.

Exhibitor briefing gets an "After the show" section (feedback, what has
been filed since); traceability.md opens with the market signal; roadmap
item 1 notes it as supply-side evidence, with buyer prices still missing;
README project status updated (show attended, Payap lead).

docs/suppliers/making-vinyl-europe-2026-exhibitors.md

@@ -11,6 +11,24 @@ Company facts are from vendor sites and the Making Vinyl channels, checked
 are written against this repo's open items (roadmap Phase 1 quotes, the
 traceability spec, the steam decision, the Thai PVC lead, the 50/50 fleet).
 
+## After the show
+
+- **Traceability drew the strongest reaction.** Most people Alexander
+  talked to in Haarlem were very interested in the plan's full traceability
+  ([traceability](../traceability.md), [digital factory](../digital-factory.md)).
+- **Sibert**: traceability was one of the reasons Sibert's representative
+  was willing to talk to us at all; without it he would strongly advise
+  against the plan. Seeing buildfor.life's software development and data
+  work made it clear to him that the project comes from the right
+  direction. For the pitch to suppliers and investors, the data and
+  control side is what makes a newcomer credible, so it leads.
+- **Filed since**: the Newbilt flyers
+  ([pressing line](../equipment/pressing-line.md)), Sibert's VS
+  specifications and Pheenix Alpha's electroforming flyers
+  ([galvanics and stamper prep](../equipment/galvanics.md)).
+
+The briefing below is kept as written before the show.
+
 ## Priority order for the three days
 
 1. **Newbilt** and **Pheenix Alpha**: the pressing-line decision. Both must