refactor: remove video channel type, fix invisible CreateChannel inputs

Voice channels already support video/screen share, so the separate video
type was redundant. Adds migration to convert existing video channels.
Also adds border-border-soft to CreateChannel input fields for visibility.

packages/shared/src/types.ts

@@ -123,7 +123,7 @@ export interface SpaceFolder {
 
 // ─── Channel Types ──────────────────────────────────────────────────────────
 
-export type ChannelType = 'text' | 'voice' | 'video';
+export type ChannelType = 'text' | 'voice';
 
 export interface Channel {
   id: string;