feat(web): improve web build configuration and accessibility

- Add source maps and web renderer build arguments with defaults
- Configure Caddy with CSP headers, cache policies, and service worker handling
- Defer loading of import screen for performance optimization
- Add semantic labels to icons for accessibility
- Update web index.html with Swedish language, meta tags, and description
- Add robots.txt and lighthouse configuration
- Add new planning documents and archive entries

flutter/Caddyfile

@@ -1,10 +1,30 @@
-:{$PORT:5000} {
-    root * /usr/share/caddy
-
-    # Proxy API calls to backend service on the internal Docker network.
-    handle /api/* {
-        reverse_proxy recipe-api:8080
-    }
+:{$PORT:5000} {
+    root * /usr/share/caddy
+
+    header {
+        Content-Security-Policy "default-src 'self'; base-uri 'self'; object-src 'none'; frame-ancestors 'self'; script-src 'self' 'unsafe-inline'; style-src 'self' 'unsafe-inline'; img-src 'self' data: blob:; font-src 'self' data:; connect-src 'self' https: http: ws: wss:; worker-src 'self' blob:"
+    }
+
+    @staticAssets {
+        path *.js *.wasm *.woff *.woff2 *.ttf *.otf
+    }
+    header @staticAssets Cache-Control "public, max-age=86400"
+
+    @hashedAssets {
+        path_regexp hashedAssets .*[._-][0-9a-fA-F]{8,}\.(js|css|wasm|woff2?|ttf|otf)$
+    }
+    header @hashedAssets Cache-Control "public, max-age=31536000, immutable"
+
+    @serviceWorker path /flutter_service_worker.js /version.json
+    header @serviceWorker Cache-Control "no-cache, must-revalidate"
+
+    @index path / /index.html
+    header @index Cache-Control "public, max-age=300, must-revalidate"
+
+    # 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
     handle {