fix: add fallback for separate language documents in API

When requesting a translation via ?lang=de or ?lang=fr, the API now:
1. First checks for embedded translations (document.translations.de/fr)
2. Falls back to checking for separate documents with -de/-fr suffix

This allows the glossary translations (glossary-de, glossary-fr) to work
with the standard /api/documents/glossary?lang=de endpoint.

Fixes the 404 error when switching languages on /docs.html page.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

src/controllers/documents.controller.js

@@ -110,7 +110,7 @@ async function getDocument(req, res) {
         });
       }
 
-      // Check if translation exists
+      // Check if translation exists (embedded in document)
       if (document.translations && document.translations[lang]) {
         const translation = document.translations[lang];
 
@@ -133,14 +133,30 @@ async function getDocument(req, res) {
           success: true,
           document: translatedDoc
         });
-      } else {
+      }
-        // Translation not available
+
-        return res.status(404).json({
+      // FALLBACK: Check for separate language document (e.g., glossary-de, glossary-fr)
-          error: 'Not Found',
+      // Try appending language code to slug
-          message: `Translation not available for language: ${lang}`,
+      const translatedSlug = `${identifier}-${lang}`;
-          available_languages: Object.keys(document.translations || {})
+      const translatedDoc = await Document.findBySlug(translatedSlug);
+
+      if (translatedDoc) {
+        return res.json({
+          success: true,
+          document: {
+            ...translatedDoc,
+            language: lang,
+            sections: undefined // Force traditional view
+          }
         });
       }
+
+      // Translation not available
+      return res.status(404).json({
+        error: 'Not Found',
+        message: `Translation not available for language: ${lang}`,
+        available_languages: Object.keys(document.translations || {})
+      });
     }
 
     // Default: Return English version