feat: scaffold PulseNode dashboard (M1)

Next.js 16 + TypeScript + Tailwind v4 app with a YAML-driven config
system: schema validation (zod), .env interpolation, and a widget
registry rendering bookmark/search/group widgets. CSS custom
properties (--pn-*) drive theming and are overridable from
config.yml's theme.variables. Config load errors surface as a
readable error page instead of crashing the app.

Hot reload, docker/system/http collectors, and the WebSocket push
layer land in later milestones per the approved plan.

config/.env.example

@@ -0,0 +1,12 @@
+# Public hostnames of the services PulseNode links to / monitors.
+# These are not secrets, but keeping them here (rather than hardcoded in
+# config.yml) means the same config.yml works across environments.
+TRAEFIK_HOST_TRAEFIK=traefik.example.com
+TRAEFIK_HOST_CODE=code.example.com
+TRAEFIK_HOST_COOLIFY=coolify.example.com
+TRAEFIK_HOST_GITEA=git.example.com
+TRAEFIK_HOST_HEADSCALE=headscale.example.com
+TRAEFIK_HOST_IMMICH=photos.example.com
+TRAEFIK_HOST_N8N=n8n.example.com
+TRAEFIK_HOST_PASSBOLT=passbolt.example.com
+TRAEFIK_HOST_UMAMI=analytics.example.com