feat(web): move Hire Us pricing to $400/hour metered billing (PRD 0002)

Replaces the $250/week retainer with a $400/hour rate billed against actual
hours, invoiced through CoinPay after the client approves them. A 10-hour
minimum engagement replaces the week as the unit of commitment.

The weekly price lived in 12 places, not the 3 the PRD listed: the front-page
Hire Us section, the Top-Level Pages list, /hire-us metadata, /pricing
(metadata, two FAQ answers, rate bullet), /about, llms.txt, skill.md, and the
Hire Us form success message.

Metered billing rather than a committed weekly block, because the old
"recurring CoinPay invoice" copy documented a mechanic that never existed:
/api/payments/create makes a single one-shot payment, not a subscription.

- coinpay-checkout derives amount_usd from hours x 400 instead of a hardcoded
  250, validates hours as quarter-hour increments at or above the minimum, and
  returns 422 before calling CoinPay on bad input. Payment metadata carries
  billing/hours/rate_usd_per_hour in place of interval.
- project-request returns a rate, billing mode, and minimum; no amount exists
  until hours are approved.
- CoinPay config block documents COINPAY_RATE_USD_PER_HOUR / COINPAY_BILLING /
  COINPAY_MINIMUM_HOURS instead of a weekly amount and interval.
- New real /terms route replacing the SPA stub: what is billable, the
  approve-then-invoice flow, the minimum, cancellation on one week's notice,
  and an explicit clause that existing engagements keep their terms until both
  sides agree in writing.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

apps/logicsrc-web/src/components/home-interactivity.tsx

@@ -45,7 +45,7 @@ export function HomeInteractivity(): null {
         }
 
         result.replaceChildren(
-          buildParagraph("Request received. If it is a fit, we will send a $250/week recurring CoinPay invoice.")
+          buildParagraph("Request received. If it is a fit, we will scope the work and invoice approved hours at $400/hour via CoinPay.")
         );
       } catch (error) {
         result.replaceChildren(