Add end-to-end process flow document and diagram; floor loading criterion

- docs/process-flow.md: mermaid chart plus stage table of every check and
  the three artist approval gates, from audio intake to fulfillment
- docs/process-flow.drawio with PNG and PDF exports
- pressing-line.md: floor must carry multiple tons per m2 in machine areas
- README: process-flow entry in document index and layout tree

docs/equipment/pressing-line.md

@@ -40,5 +40,14 @@ electrical load, saturated steam at 10 bar, and compressed air and cooling
 water circuits, plus side rooms for materials, compressor, chiller, and
 finished goods.
 
+**Floor loading is a building-selection criterion**: the slab must carry
+multiple tons per m² in the machine areas. A Newbilt press weighs 1,350 kg
+on a footprint under 1 m², and the boiler, chiller, hydraulic aggregate,
+battery stack, and stacked material storage all concentrate weight the same
+way. The floor must also be flat but not slippery (machine levelling pads
+need grip) and resistant to the solvents used in production. Dynamic loads
+from press cycles come on top of the static figures, so the structural
+engineer gets the vendor data sheets, not just the totals.
+
 Source documents live in [`newbilt/`](newbilt/): the budgetary offer, the
 Duplex site requirements, the process schematic, and the service rate card.