feat: update API base URL handling and improve Caddy configuration for Flutter app

flutter/Caddyfile

@@ -1,9 +1,16 @@
 :{$PORT:5000} {
     root * /usr/share/caddy
-    file_server
+
+    # Proxy API calls to backend service on the internal Docker network.
+    handle /api/* {
+        reverse_proxy recipe-api:8080
+    }
 
     # SPA-routing – returnera alltid index.html för okända paths
-    try_files {path} /index.html
+    handle {
+        try_files {path} /index.html
+        file_server
+    }
 
     encode gzip
 }

flutter/Dockerfile

@@ -8,10 +8,11 @@ RUN flutter pub get
 
 COPY . .
 
-# Inject the internal API URL at build time via --dart-define
-ARG FLUTTER_API_URL_INTERNAL=http://recipe-api:8080
+# Inject API base URL at build time via --dart-define.
+# Default to same-origin /api to avoid mixed-content in HTTPS deployments.
+ARG API_BASE_URL=/api
 RUN flutter build web --release \
-    --dart-define=API_BASE_URL=${FLUTTER_API_URL_INTERNAL}
+    --dart-define=API_BASE_URL=${API_BASE_URL}
 
 # Stage 2 – Serve with Caddy
 FROM caddy:alpine AS runner

flutter/lib/core/api/api_client.dart

@@ -1,8 +1,8 @@
 import 'package:http/http.dart' as http;
 
-/// Platform-neutral HTTP client wrapping the internal API base URL.
-/// Base URL is read from the FLUTTER_API_URL_INTERNAL environment variable
-/// (set by Docker) or falls back to localhost for local development.
+/// Platform-neutral HTTP client.
+/// API base URL is injected at build time via --dart-define=API_BASE_URL.
+/// Default is same-origin '/api' to avoid mixed-content on HTTPS sites.
 class ApiClient {
   final String baseUrl;
   final http.Client _client;
@@ -10,7 +10,7 @@ class ApiClient {
   ApiClient({http.Client? client})
       : baseUrl = const String.fromEnvironment(
           'API_BASE_URL',
-          defaultValue: 'http://localhost:8080',
+                    defaultValue: '/api',
         ),
         _client = client ?? http.Client();