feat: LinkedIn video upload working + static file serving

- Add /public static route to serve files from /vaults/public
- Fix LinkedIn API version: 202501 → 202603 (active version)
- OpenAPI schema already included POST /api/linkedin/video
- Successfully posted Remotion video to LinkedIn

src/clients/linkedin.ts

@@ -133,7 +133,7 @@ async function linkedinRestRequest(
     headers: {
       'Authorization': `Bearer ${accessToken}`,
       'Content-Type': 'application/json',
-      'LinkedIn-Version': '202501',
+      'LinkedIn-Version': '202603',
       'X-Restli-Protocol-Version': '2.0.0',
     },
     body: body ? JSON.stringify(body) : undefined,
@@ -224,7 +224,7 @@ export async function createVideoPost(
       headers: {
         'Authorization': `Bearer ${accessToken}`,
         'Content-Type': 'application/json',
-        'LinkedIn-Version': '202501',
+        'LinkedIn-Version': '202603',
         'X-Restli-Protocol-Version': '2.0.0',
       },
       body: JSON.stringify({