feat: HIVE_DESKTOP_MODE env to skip frontend build in hive serve

When `hive serve` is launched from a desktop shell (Electron), the
client ships its own UI and the bundled environment usually has no
`npm` toolchain. Building the React frontend fails noisily and isn't
needed.

Setting `HIVE_DESKTOP_MODE=1` in the spawn env now short-circuits
`_build_frontend()` cleanly. The flag also serves as a hook for
future desktop-vs-server branching (single-user mode, telemetry,
etc.) without needing a new env var each time.

Default (unset) preserves today's behavior — no change for server
deployments.

core/framework/config.py

@@ -14,6 +14,16 @@ from typing import Any
 
 DEFAULT_MAX_TOKENS = 8192
 
+# ---------------------------------------------------------------------------
+# Desktop mode
+# ---------------------------------------------------------------------------
+# Set by the Electron shell when it spawns `hive serve` so the runtime knows
+# it's hosted inside a desktop client rather than served standalone. Today
+# this only gates the frontend-build step in `hive serve` (the desktop ships
+# its own renderer), but it's also a useful hook for future single-user /
+# telemetry-off branching.
+DESKTOP_MODE: bool = bool(os.environ.get("HIVE_DESKTOP_MODE"))
+
 # ---------------------------------------------------------------------------
 # Hive home directory structure
 # ---------------------------------------------------------------------------

core/framework/loader/cli.py

@@ -92,7 +92,13 @@ def cmd_serve(args: argparse.Namespace) -> int:
 
     from aiohttp import web
 
-    _build_frontend()
+    from framework.config import DESKTOP_MODE
+
+    # Skip frontend build when running inside the desktop shell — Electron
+    # ships its own renderer, and running `npm` from a packaged install
+    # often fails (no toolchain on the user's machine).
+    if not DESKTOP_MODE:
+        _build_frontend()
 
     from framework.observability import configure_logging
     from framework.server.app import create_app