Add revenue model: 3.2M-5.9M EUR/yr at full capacity, per-record economics

Blended pressing price, direct cost breakdown, margin, EBITDA and payback
bands; all arithmetic reviewer-recomputed; adverse payback corner stated
honestly alongside mid assumptions

README.md

@@ -95,6 +95,9 @@ The detail lives in dedicated documents:
 - [Total investment](docs/finance/total-investment.md): the full-vision
   roll-up (~4M to 7.7M EUR) and the ~1.5M to 2.5M EUR phased entry, with
   the basis of every block
+- [Revenue model](docs/finance/revenue-model.md): rough full-capacity
+  revenue (~3.2M to 5.9M EUR/yr), direct cost and margin per record, and
+  the levers and caveats behind the numbers
 
 ## Repository Layout