fix(docker): Build Tailwind CSS in Docker image

The /style.css route 500'd in production because style.css is
gitignored and the Dockerfile never produced it: only main.py and
templates/ were copied into the image.

Mirror the myice Dockerfile by building the CSS in the builder stage:
copy the tailwind input files, download the standalone Tailwind CLI
(arch-aware for x64/arm64), and compile style.css. The artifact is
then copied into the runtime stage.

build-css.sh is kept for local dev but not used in Docker because its
#!/bin/bash shebang and pipefail are incompatible with alpine's sh.

Dockerfile

@@ -23,6 +23,18 @@ RUN apk add --no-cache gcc musl-dev libffi-dev openssl-dev
 COPY requirements.txt .
 RUN pip install --no-cache-dir -r requirements.txt
 
+# Build Tailwind CSS
+COPY templates/index.html templates/index.html
+COPY style-input.css tailwind.config.js ./
+RUN case "$(uname -m)" in \
+        x86_64) arch="x64" ;; \
+        aarch64|arm64) arch="arm64" ;; \
+        *) echo "Unsupported architecture: $(uname -m)"; exit 1 ;; \
+    esac \
+    && curl -sL "https://github.com/tailwindlabs/tailwindcss/releases/download/v3.4.17/tailwindcss-linux-${arch}" -o tailwindcss \
+    && chmod +x tailwindcss \
+    && ./tailwindcss -i ./style-input.css -o ./style.css --minify
+
 #############################################
 # Final stage
 #############################################
@@ -35,6 +47,7 @@ COPY --from=builder /usr/local/bin /usr/local/bin
 # Copy application files
 COPY main.py .
 COPY templates/ templates/
+COPY --from=builder /app/style.css ./style.css
 
 # Change ownership to non-root user
 RUN chown -R app:app /app