fix cert and image display issues

Dockerfile.dev

@@ -63,6 +63,27 @@ RUN wget -O /usr/local/bin/mkcert https://github.com/FiloSottile/mkcert/releases
     && chmod +x /usr/local/bin/mkcert
 
 # Create certificates directory and generate localhost certificates
+# ============================================================================
+# IMPORTANT: Certificate includes MULTIPLE hostnames (SANs)
+# ============================================================================
+# The certificate is generated for 'localhost', '127.0.0.1', AND '::1' because:
+#
+# 1. Users may access the site via https://localhost/ OR https://127.0.0.1/
+# 2. Database stores image URLs using one hostname (typically 127.0.0.1)
+# 3. The seed script uses https://127.0.0.1 for image URLs (database constraint)
+# 4. NGINX is configured to accept BOTH hostnames (see docker/nginx/dev.conf)
+#
+# Without all hostnames in the certificate's Subject Alternative Names (SANs),
+# browsers would show ERR_CERT_AUTHORITY_INVALID when loading images or other
+# resources that use a different hostname than the one in the address bar.
+#
+# The mkcert command below creates a certificate valid for all three:
+#   - localhost     (IPv4 hostname)
+#   - 127.0.0.1     (IPv4 address)
+#   - ::1           (IPv6 loopback)
+#
+# See also: docker/nginx/dev.conf, docs/FLYER-URL-CONFIGURATION.md
+# ============================================================================
 RUN mkdir -p /app/certs \
     && cd /app/certs \
     && mkcert -install \