refactor(web): collapse the shell boot into the AppWebEntry class

The four free functions in boot.tsx become one kernel class holding what
must exist before cordis: the parsed BootManifest, the ClientModuleSystem
instance, and the loading-page handles. Context/Loader setup runs in
parallel with the immediately-tier prefetch, but entry creation awaits the
prefetch: materialization is tree.import's synchronous require, so
cross-package require edges (i18n -> runtime/client) need every
immediately-tier factory registered first — unbarriered creation raced
10-25% of boots. The kernel adopts the modules entry (writes the
__DSH_MODULES__ slot pre-cordis, creates the entry first, skips its graph
row), and provide('modules') now lives in the adoption apply. apps/web
drops its host-package edges (composition is apps/cli's job).

apps/web/tests/support.ts

@@ -16,10 +16,7 @@ export function requireDist(): void {
   }
 }
 
-/**
- * OS-assigned free port, released before use. startWebServer echoes
- * options.port instead of the bound one, so passing 0 directly is unusable.
- */
+/** OS-assigned free port, released before use (the spawned `dsh web` needs a concrete --port). */
 export function probeFreePort(): Promise<number> {
   return new Promise((resolvePort, reject) => {
     const probe = createServer()