fix: remove fallback content, fix video upload and positioning

- Remove hardcoded fallback data — DB is sole content source
- Sections render conditionally when data exists
- Hero video slots save after each upload (not only when all 3 filled)
- Video positions preserved (left/center/right) with empty string slots
- Client-side 10MB hard limit on video uploads with clear error
- Server-side upload error handling for body size limits
- Guard Team section against empty members array
- Clean up old uploaded images and videos

src/lib/content.ts

@@ -1,11 +1,10 @@
 import { getSiteContent } from "@/lib/db";
-import { siteContent as fallback } from "@/data/content";
 import type { SiteContent } from "@/types/content";
 
 let cached: { data: SiteContent; expiresAt: number } | null = null;
 const CACHE_TTL = 5 * 60 * 1000; // 5 minutes
 
-export function getContent(): SiteContent {
+export function getContent(): SiteContent | null {
   const now = Date.now();
   if (cached && now < cached.expiresAt) {
     return cached.data;
@@ -17,9 +16,9 @@ export function getContent(): SiteContent {
       cached = { data: content, expiresAt: now + CACHE_TTL };
       return content;
     }
-    return fallback;
+    return null;
   } catch {
-    return fallback;
+    return null;
   }
 }