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/Dockerfile

@@ -14,11 +14,20 @@ RUN flutter gen-l10n
 # Run tests
 RUN flutter test
 
-# 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=${API_BASE_URL}
+# Inject API base URL at build time via --dart-define.
+# Default to same-origin /api to avoid mixed-content in HTTPS deployments.
+ARG API_BASE_URL=/api
+ARG SOURCE_MAPS=false
+ARG WEB_RENDERER=auto
+RUN set -eux; \
+    build_args="--release --dart-define=API_BASE_URL=${API_BASE_URL}"; \
+    if [ "${SOURCE_MAPS}" = "false" ]; then \
+      build_args="${build_args} --no-source-maps"; \
+    fi; \
+    if [ "${WEB_RENDERER}" != "auto" ]; then \
+      build_args="${build_args} --web-renderer=${WEB_RENDERER}"; \
+    fi; \
+    flutter build web ${build_args}
 
 # Stage 2 – Serve with Caddy
 FROM caddy:alpine AS runner