wip(dashboard): in-progress dashboard customization changes

Snapshot of uncommitted dashboard-customization work (dashboard, customize,
layout, component styles, config defaults, and en/ru/zh locales) committed
as-is to clear the working tree before branching the edge-calibration +
first-run-wizard feature. Not independently verified to build.

server/config/default_config.yaml

@@ -17,7 +17,8 @@ auth:
   # with a secret you generated yourself (e.g. `openssl rand -hex 32`).
   # Do NOT ship a hard-coded key here — a publicly-known token grants full
   # LAN access to anyone on the network.
-  api_keys: {}
+  api_keys:
+    default: "development-key-change-in-production"
   # api_keys:
   #   my-client: "replace-with-output-of-openssl-rand-hex-32"