SEO: add crawlable language navigation links for Google indexing

- Add sr-only CSS class for screen-reader/crawler-visible elements
- Add hidden <nav> with real <a> links to all 6 language versions in template.html
- Googlebot can now discover /de/, /fr/, /es/, /pt-BR/, /ru/ via HTML links
- No visual changes - existing <select> dropdown remains the user-facing switcher
- Rebuild all www/ output with updated CSS hash

package-lock.json

@@ -1240,6 +1240,7 @@
       "integrity": "sha512-UVJyE9MttOsBQIDKw1skb9nAwQuR5wuGD3+82K6JgJlm/Y+KI92oNsMNGZCYdDsVtRHSak0pcV5Dno5+4jh9sw==",
       "dev": true,
       "license": "MIT",
+      "peer": true,
       "bin": {
         "acorn": "bin/acorn"
       },
@@ -1373,6 +1374,7 @@
       "integrity": "sha512-riJjyv1/mHLIPX4RwiK+oW9/4c3TEUeORHKefKAKnZ5kyslbN+HXowtbaVEqt4IMUB7OXlfixcs6gsFeo/jhiQ==",
       "dev": true,
       "license": "Apache-2.0",
+      "peer": true,
       "peerDependencies": {
         "bare-abort-controller": "*"
       },
@@ -1895,6 +1897,7 @@
       "integrity": "sha512-loXy6bWOoP3EP6JA7jo6p5jMpBJmHmsNZM5SFRHLdh1MGOPurMnNBj4ZlAbaqUAaQWbCr7jHV4P7gzAyryZWkQ==",
       "dev": true,
       "license": "MIT",
+      "peer": true,
       "dependencies": {
         "@eslint-community/eslint-utils": "^4.8.0",
         "@eslint-community/regexpp": "^4.12.2",