Expose gateway billing flows from the synced server baseline

The preserved local work adds PopiNewAPI billing checkout, gateway account binding, and matching web console/pricing surfaces on top of the current test-server baseline. During the merge, the start-end video helpers from the deployed baseline were kept alongside the actionGenerate prompt handling from the WIP.

Constraint: Current usable baseline is 7054436, already deployed on the test server.

Rejected: Commit the WIP before syncing the baseline | would have hidden conflicts with the deployed start-end-frame changes.

Confidence: medium

Scope-risk: broad

Directive: Do not deploy this commit to the test server without rechecking gateway credentials and billing checkout behavior in that environment.

Tested: go test ./...

Tested: make build

Tested: cd web && npm run build

web/components/site-chrome.tsx

@@ -44,6 +44,7 @@ export async function SiteChrome({
             skills: liveCopy.nav.skills,
             console: dictionary.nav.console,
             pricing: dictionary.nav.pricing,
+            billing: locale === "zh" ? "账单" : "Billing",
           }}
           locale={locale}
         />
@@ -74,6 +75,7 @@ export async function SiteChrome({
           <Link href={localize(locale, "/docs")}>{dictionary.nav.docs}</Link>
           <Link href={localize(locale, "/skills")}>{liveCopy.nav.skills}</Link>
           <Link href={localize(locale, "/pricing")}>{dictionary.nav.pricing}</Link>
+          <Link href={localize(locale, "/billing")}>{locale === "zh" ? "账单" : "Billing"}</Link>
           <Link href={localize(locale, "/console")}>{dictionary.nav.console}</Link>
         </div>
       </footer>