Add docs link in sidebar, Dockerfile for VitePress, make Keycloak optional

- Add external "Docs" link in sidebar with configurable DOCS_URL
- Add Dockerfile.docs for VitePress static site (nginx)
- Add DOCS_URL build arg to Dockerfile.dashboard
- Run cargo fmt

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

Dockerfile.dashboard

@@ -2,8 +2,11 @@ FROM rust:1.89-bookworm AS builder
 
 RUN cargo install dioxus-cli --version 0.7.3
 
+ARG DOCS_URL=/docs
+
 WORKDIR /app
 COPY . .
+ENV DOCS_URL=${DOCS_URL}
 RUN dx build --release --package compliance-dashboard
 
 FROM debian:bookworm-slim