refactor(webserver): extract SPA dist serving to the frontend-static fallback seat

The webserver's built-in static dist serving becomes a single-owner fallback
seat (registerFallback/applyIndexTaps); the SPA server moves to the new
@deepseek-ai/dsh-frontend-static plugin so the composing application owns its
dist as composition, not carrier config. distIndex leaves the webserver
schema; unclaimed fallback answers 404.

tsconfig.host.json

@@ -185,6 +185,9 @@
     { "path": "./packages/support/agent-loop-testkit" },
     { "path": "./packages/acp/acp" },
     { "path": "./packages/examples/acp-demo" },
+    { "path": "./packages/bundle/base" },
+    { "path": "./packages/bundle/headless" },
+    { "path": "./packages/bundle/web-app" },
     { "path": "./packages/ui/app-boot" },
     { "path": "./packages/ui/jsonrpc" },
     { "path": "./packages/examples/jsonrpc-demo" },
@@ -228,6 +231,7 @@
     // client aggregate's webserver reference.
     { "path": "./packages/host/directory-picker-browse" },
     { "path": "./packages/host/directory-picker-native" },
+    { "path": "./packages/host/frontend-static" },
     { "path": "./packages/host/webserver" },
     { "path": "./packages/sdk/sdk-client" },
     { "path": "./packages/sdk/helper" },