Business plan: isometric calculator views instead of FreeCAD, software section with screenshots

- Cover and section 6.2 now use the isometric plant view of the plant and
  business plan calculator, drawn with each version's own preset: the
  cover (roofs, no labels), Figure 8 the site from above, Figure 9 the
  ground floor cut open, Figure 10 the press hall close up. The FreeCAD
  aerial render, the Mueang Chi site plan and the hall layout sketch are
  no longer in the plan; the captions say the calculator draws the Payap
  scenario model while the 6.2 text and zone table are the Mueang Chi
  hall.
- New section 5.5 "The software: plant overview, factory console and
  artist platform" with six screenshots of the demos: the plant overview
  (simulated SCADA), the factory console press floor and its ERPNext
  link, the artist ordering offer, fan funding and the record passport.
  Simulated data is marked as such; the platform name stays undecided.
- Figures renumbered (budget card 11, cash 12) and named in the
  section 15 source table. Renders in docs/renders/calculator/ and
  docs/renders/demos/; README bullet updated.

README.md

@@ -305,8 +305,11 @@ The detail lives in dedicated documents:
   one table comparing it with the other, both priced without contingency
   and with the ramp-up reserve. Each carries renders of the
   [plant and business plan calculator](docs/fleet-calculator.html) with
-  its own preset (plant view, budget check, ten years of cash; in
-  `docs/renders/calculator/`). Built from `docs/business-plan/build/`
+  its own preset (the isometric plant view on the cover and in section 6,
+  the budget check, ten years of cash; in `docs/renders/calculator/`) and
+  a software section (5.5) with screenshots of the plant overview, the
+  factory console with its ERPNext link, the artist ordering demo, fan
+  funding and the record passport (`docs/renders/demos/`). Built from `docs/business-plan/build/`
   (`python build_plan.py` makes both versions; the PDFs are exported with
   LibreOffice so the table of contents is filled in). Draft 0.2, a single
   launch-plant plan with contingency, is in the git history