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>

api/rest.py

@@ -1,3 +1,5 @@
+import os
+from pathlib import Path
 from typing import Any
 
 from api.console import create_console_router
@@ -25,7 +27,27 @@ def create_app(
 ) -> Any:
     from fastapi import BackgroundTasks, FastAPI, HTTPException
     from fastapi.middleware.cors import CORSMiddleware
+    from fastapi.responses import RedirectResponse
+    from fastapi.staticfiles import StaticFiles
     from pydantic import BaseModel
+    from starlette.exceptions import HTTPException as StarletteHTTPException
+    from starlette.types import Scope
+
+    class SpaStaticFiles(StaticFiles):
+        """``StaticFiles`` variant that falls back to ``index.html`` for SPA routes.
+
+        Mirrors ``apps/cloud-api/cloud_api/app.py``'s implementation: an unknown
+        path like ``/ui/tasks/abc`` would otherwise 404 instead of letting the
+        SPA's client-side router handle it.
+        """
+
+        async def get_response(self, path: str, scope: Scope) -> Any:
+            try:
+                return await super().get_response(path, scope)
+            except StarletteHTTPException as exc:
+                if exc.status_code == 404 and path != "index.html":
+                    return await super().get_response("index.html", scope)
+                raise
 
     device_manager = manager or DEFAULT_MANAGER
     store = metadata_store or TaskMetadataStore()
@@ -127,6 +149,24 @@ def create_app(
         )
     )
 
+    console_static_dir = os.environ.get("RUNTIME_CONSOLE_STATIC_DIR")
+    if console_static_dir:
+        dist_dir = Path(console_static_dir)
+        if not dist_dir.is_dir():
+            raise ValueError(
+                f"RUNTIME_CONSOLE_STATIC_DIR is not a directory: {dist_dir}"
+            )
+
+        @app.get("/", include_in_schema=False)
+        async def _redirect_to_console() -> RedirectResponse:
+            return RedirectResponse(url="/ui/")
+
+        app.mount(
+            "/ui",
+            SpaStaticFiles(directory=str(dist_dir), html=True),
+            name="console",
+        )
+
     return app