feat(web): tane.comunes.org landing + localized app screenshots

- Hugo site (site/): EN/ES intro + legal (generated from docs/legal), an
  ES/EN About page from docs/{que-es-tane,what-is-tane}.md, seed-green theme,
  responsive header, store-badge placeholders, multi-stage Hugo->nginx image.
- Golden screenshot harness (test/screenshots/): en,es,fr,de,pt,ja + RTL demo,
  real fonts via DejaVu Sans + FontManifest; skip-by-default tag so CI stays
  green. collect_screenshots.sh feeds site/ and fastlane phoneScreenshots.
- Drop editorial notes from the public explainer.

site/layouts/partials/lang-switch.html

@@ -0,0 +1,16 @@
+{{- /* Links to this page in the other language; falls back to that language's home. */ -}}
+<span class="lang-switch">
+  {{- range .Site.Languages -}}
+    {{- $lang := . -}}
+    {{- if eq $lang.Lang $.Site.Language.Lang -}}
+      <span class="lang current" aria-current="true">{{ $lang.LanguageName }}</span>
+    {{- else -}}
+      {{- $target := "" -}}
+      {{- range $.AllTranslations -}}
+        {{- if eq .Language.Lang $lang.Lang -}}{{- $target = .RelPermalink -}}{{- end -}}
+      {{- end -}}
+      {{- if not $target -}}{{- $target = ($lang.Lang | printf "/%s/" | relURL) -}}{{- end -}}
+      <a class="lang" href="{{ $target }}" lang="{{ $lang.LanguageCode }}">{{ $lang.LanguageName }}</a>
+    {{- end -}}
+  {{- end -}}
+</span>