Fix basic auth: use htpasswd instead of openssl passwd

openssl passwd -apr1 produces inconsistent output in nginx:alpine.
Switch to htpasswd from apache2-utils which is the standard tool.

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

Dockerfile

@@ -12,6 +12,8 @@ RUN npm run build
 # ── Stage 2: serve ──────────────────────────────────────────────────────────
 FROM nginx:alpine
 
+RUN apk add --no-cache apache2-utils
+
 # Copy built assets
 COPY --from=builder /app/dist /usr/share/nginx/html