ui redesign, markdown fix + metadata and auth header

backend/Dockerfile

@@ -1,14 +1,30 @@
-FROM rust:latest as builder
+FROM rust:1.83-slim AS builder
 
 WORKDIR /usr/src/app
-COPY . .
 
+# Cache deps as their own layer.
+COPY Cargo.toml Cargo.lock ./
+RUN mkdir -p src \
+    && echo "fn main() {}" > src/main.rs \
+    && cargo build --release \
+    && rm -rf src target/release/deps/backend* target/release/backend*
+
+# Now build the real source.
+COPY src ./src
 RUN cargo build --release
 
 FROM debian:bookworm-slim
 
+RUN apt-get update \
+    && apt-get install -y --no-install-recommends ca-certificates curl \
+    && rm -rf /var/lib/apt/lists/* \
+    && groupadd --system --gid 1000 app \
+    && useradd --system --uid 1000 --gid app --home-dir /app app
+
 WORKDIR /app
 COPY --from=builder /usr/src/app/target/release/backend /usr/local/bin/backend
 
+USER app:app
+
 EXPOSE 3000
 CMD ["backend"]