feat(host-agent): serve built console via SPA-aware static mount

Add an optional single-process mode where the backend serves the built
console bundle itself, so operators don't need a separate `npm run dev`
for edge/dev setups. When RUNTIME_CONSOLE_STATIC_DIR points at the
console dist directory, the app mounts a SpaStaticFiles handler at /ui/
(with 404 fallback to index.html for client-side routing) and redirects
/ to /ui/. The console build uses an empty VITE_API_BASE_URL for relative
API paths (same-origin, no CORS), and Vite's base is set to /ui/ so
assets resolve under the mount. /console/* JSON API is unchanged and is
shared by both serve modes.

api.ts now treats an explicitly-empty VITE_API_BASE_URL as "use relative
paths" instead of falling back to the dev default, which previously
forced absolute URLs even in same-origin builds.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

console/README.md

@@ -28,3 +28,19 @@ for local frontend development.
 ```bash
 npm run build
 ```
+
+## Same-Origin, Single-Process Mode
+
+For an edge/dev setup where running a separate `npm run dev` process is too heavy,
+the backend can serve the built console directly from the same process:
+
+```bash
+VITE_API_BASE_URL= npm run build
+RUNTIME_CONSOLE_STATIC_DIR=$(pwd)/dist uvicorn api.rest:create_app --factory --host 127.0.0.1 --port 8000
+```
+
+`VITE_API_BASE_URL=` (empty) makes the build use relative API paths so it works
+same-origin without CORS. The console is then served at `/ui/` (with `/`
+redirecting there); `/console/*` remains the JSON API used by both this mode
+and local `npm run dev`. Rebuild (`npm run build`) after frontend changes —
+this mode does not hot-reload.