fix(headless): CI green + review-bot findings for the shared composition

Coverage: api-proxy.ts joins the web-transport exclusion block (its
behavior specs moved here with it; the assembled-entry coverage lands with
the GUI test lane). Static: config-catalog regenerated after the log-round
revert shifted a source anchor. Prose brought current per review: the cli
README now describes the one shared composition (and its build
prerequisite), the apiproxy README points at the api-gateway row instead of
the deleted runtime package, and the config-tree agent note's headless
deferral paragraph records what actually landed (bilingual pair
re-recorded).

vitest.config.ts

@@ -123,6 +123,7 @@ export default defineConfig({
         'packages/client/connection/src/http-bridge.ts',
         'packages/host/apiproxy/src/index.ts',
         'packages/host/apiproxy/src/invariant.ts',
+        'packages/host/apiproxy/src/api-proxy.ts',
         ...windowsUnsupportedPackages.map(path => `${path}/src/**/*.ts`),
         ...windowsCoverageExclusions,
       ],