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/lighthouse/README.md

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+# Lighthouse protocol for Flutter web
+
+Detta dokument implementerar en reproducerbar baseline/eftermatning enligt planen i `.kilo/plans/1779550355555-hidden-mountain.md`.
+
+## 1) Fast matprofil (anvand samma varje gang)
+
+- URL: samma exakta URL per miljo (`http://localhost:5000` respektive produktion).
+- Form factor: `mobile`.
+- Lighthouse-kategorier: `performance`, `accessibility`, `seo`.
+- Antal korningar: minst 3 per miljo.
+- Throttling: `simulate` (Lighthouse standard, konstant mellan korningar).
+
+## 2) Korningar
+
+Lokal container:
+
+```bash
+docker compose -f compose.yml -f compose.flutter.yml up -d --build recipe-api recipe-flutter
+node flutter/lighthouse/collect.mjs --url http://localhost:5000 --label local-baseline --runs 3 --form-factor mobile
+```
+
+Produktion:
+
+```bash
+node flutter/lighthouse/collect.mjs --url https://DIN-DOMAN --label prod-baseline --runs 3 --form-factor mobile
+```
+
+Resultat skrivs till `flutter/lighthouse/results/` som:
+
+- `<label>-run-1.json`, `<label>-run-2.json`, `<label>-run-3.json`
+- `<label>-summary.json`
+- `<label>-summary.md`
+
+## 3) Baseline-tabell (fylls med faktiska resultat)
+
+| Miljo | Perf median | A11y median | SEO median | LCP ms median | TBT ms median | INP ms median | Transfer KB median | Requests median |
+| --- | ---: | ---: | ---: | ---: | ---: | ---: | ---: | ---: |
+| Lokal container | TODO | TODO | TODO | TODO | TODO | TODO | TODO | TODO |
+| Produktion | TODO | TODO | TODO | TODO | TODO | TODO | TODO | TODO |
+
+## 4) Re-matning efter andringar
+
+Kor samma kommandon med nya labels, till exempel:
+
+```bash
+node flutter/lighthouse/collect.mjs --url http://localhost:5000 --label local-after --runs 3 --form-factor mobile
+node flutter/lighthouse/collect.mjs --url https://DIN-DOMAN --label prod-after --runs 3 --form-factor mobile
+```
+
+Jamor `*-summary.md` mot baseline for att verifiera:
+
+- Forbattring i minst tva nyckelmatt (exempel LCP/TBT)
+- Ingen regress i Accessibility/SEO
+
+## 5) Renderer A/B (Fas 3)
+
+`flutter/Dockerfile` och `compose.flutter.yml` har nu build-args for rendererexperiment:
+
+- `WEB_RENDERER=auto` (default)
+- `WEB_RENDERER=canvaskit`
+- `WEB_RENDERER=skwasm`
+
+Exempel (separat buildvariant):
+
+```bash
+docker compose -f compose.yml -f compose.flutter.yml build --build-arg WEB_RENDERER=canvaskit recipe-flutter
+docker compose -f compose.yml -f compose.flutter.yml up -d recipe-flutter
+node flutter/lighthouse/collect.mjs --url http://localhost:5000 --label local-canvaskit --runs 3 --form-factor mobile
+```
+
+Rollback-kriterium: behall `WEB_RENDERER=auto` om A/B inte ger tydlig forbattring i transfer size + LCP/TBT utan visuell regress.
+
+## 6) SEO routing-beslut
+
+- `robots.txt` hanteras i Flutter web app-shell (`flutter/web/robots.txt`).
+- `sitemap.xml` hanteras upstream pa domanniva eftersom absolut canonical host maste vara korrekt per miljo.