## What this PR does
Brings the enterprise procurement flow in line with the new D71 pricing,
tidies up the buyer journey, and fixes a handful of things we found
testing it end to end.
### Pricing
- Priced on the new run-based model (per PDF, per policy), USD only.
Dropped the old currency picker.
- Added the policy posture choice (Essentials / Governed / Regulated)
and show roughly how many policies each covers (~2 / ~4 / ~7).
- The live estimate in the quote builder now matches the real quote the
backend produces.
- Contracts renew each year with a fixed 3% increase. The agreement
shows this plus the first renewal figure, and we save that figure on the
quote so it can't drift later.
### Trial and journey
- Starting a trial now asks for your deployment (Cloud / Self-hosted /
Air-gapped) and team size up front, and that seeds the quote.
- Quote and agreement are now one step: you review the quote and the
agreement together and click "Accept & subscribe" once. No more
accepting a quote and then separately signing.
- "Start a trial" on the home page opens the setup popup right there
instead of sending you off to another page.
- The calculator asks for number of users again and works the volume out
from that.
- Removed the demo-only buttons (reset, simulate payment) and the "Key
documents" button (it wasn't real).
- The licence key now lives behind its own "Licence key" button instead
of being shown inside every popup.
### Air-gapped licence file
- Air-gapped teams can download their licence file (.lic) during the
trial, not only after they pay.
- The popup warns that a trial file needs re-downloading once the
agreement is done, because the file is a snapshot and doesn't refresh
itself the way the online key does.
### Fixes found while testing
- Accepting a quote now upgrades the licence from trial to full straight
away (it wasn't before).
- The "Download invoice" button keeps working after a page refresh (we
now save the invoice PDF link).
- Invoice line items read differently from each other instead of all
showing the same name.
### Notes for reviewers
- The matching backend changes (Stripe quote/accept functions, database
migrations) live in the Stirling-PDF-SaaS repo on `v3`. They ship when
we do the full v3 release.
- All checks are green.
