Add animated plant operation page (simulated SCADA overview)

docs/plant-operation.html: one self-contained static page showing the
whole plant running, from PVC intake and the material lab gate through
extruder, press cycle (load/close/steam/cool/open/eject), trimmer, 100%
optical inspection, sampled audio comparison, finishing, packaging
(matrix code vs barcode) and fulfillment. The metal path (audio intake,
mastering, cutting, silvering, father/mother/stamper, stamper prep) runs
above with the three artist gates; utilities (steam, cooling, air,
hydraulics, grinder/regrind, energy, traceability, HVAC) below with
live-looking tags.

Numbers are taken from the repo (Newbilt site requirements, scale.md,
quality-automation.md, process-flow.md). Every station is clickable for
what happens there and the checks that gate it. Two demo buttons show a
steam pressure dip holding the press and a new PVC lot held by the lab
until a test pressing releases it. README links the page.

README.md

@@ -92,6 +92,11 @@ The detail lives in dedicated documents:
 - [Process flow](docs/process-flow.md): the whole chain from audio file to
   delivered record as a chart and stage table, with every check and the
   three artist approval gates (printable diagram alongside)
+- [Plant operation page](docs/plant-operation.html): a single static page
+  animating the whole plant as a simulated SCADA overview, from PVC intake
+  and the material lab through extruder, press, trim, optical inspection,
+  finishing, packaging and fulfillment, with the metal path, utilities and
+  energy alongside; open it in a browser, every station is clickable
 - [Production timeline](docs/production-timeline.md): how long an order
   takes stage by stage, launch vs mature configuration, the repress fast
   path, and what lead time can honestly be quoted to a customer