fix(album): resolve TypeScript strict array access errors

Fix TS2345 errors where array element access (medias[i]) was inferred as
`AlbumMediaItem | undefined` instead of `AlbumMediaItem`.

Changes:
- Add non-null assertion (!) after array access in for loops
- Add explicit cast to AnyMessageContent for hasNonNullishProperty calls

The non-null assertion is safe here because we iterate with `i < medias.length`,
guaranteeing the index is valid.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/Socket/messages-send.ts

@@ -1529,7 +1529,7 @@ export const makeMessagesSocket = (config: SocketConfig) => {
 
 			// Send each media item sequentially
 			for (let i = 0; i < medias.length; i++) {
-				const media = medias[i]
+				const media = medias[i]!
 
 				const result = await sendMediaWithRetry(media, i)
 				results.push(result)