Refactor locale system: align types with usage, add CMS formatting docs (#59)

* Initial plan

* Initial analysis: understanding locale system issues

Co-authored-by: denshooter <44590296+denshooter@users.noreply.github.com>

* Fix translation types to match actual component usage

Co-authored-by: denshooter <44590296+denshooter@users.noreply.github.com>

* Add comprehensive locale system documentation and fix API route types

Co-authored-by: denshooter <44590296+denshooter@users.noreply.github.com>

* Address code review feedback: improve readability and translate comments to English

Co-authored-by: denshooter <44590296+denshooter@users.noreply.github.com>

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: denshooter <44590296+denshooter@users.noreply.github.com>

app/api/i18n/[namespace]/route.ts

@@ -14,9 +14,9 @@ const messagesMap = { en: enMessages, de: deMessages };
  */
 export async function GET(
   req: NextRequest,
-  { params }: { params: { namespace: string } }
+  { params }: { params: Promise<{ namespace: string }> }
 ) {
-  const namespace = params.namespace;
+  const { namespace } = await params;
   const locale = req.nextUrl.searchParams.get('locale') || 'en';
 
   // Normalize locale (de-DE -> de)

app/api/projects/[id]/translation/route.ts

@@ -61,12 +61,12 @@ export async function PUT(
       locale,
       title,
       description,
-      content: content ?? null,
+      content: content ?? undefined,
     },
     update: {
       title,
       description,
-      content: content ?? null,
+      content: content ?? undefined,
     },
   });