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/web/src/components/layout/ChannelSidebar.tsx

@@ -98,7 +98,7 @@ export function ChannelSidebar() {
   const canCreateInvite = hasPermissionBit(mySpacePerms, PermissionBits.CREATE_INVITE);
 
   const textChannels = channels.filter(c => c.type === 'text');
-  const voiceChannels = channels.filter(c => c.type === 'voice' || c.type === 'video');
+  const voiceChannels = channels.filter(c => c.type === 'voice');
 
   const handleChannelClick = (channelId: string) => {
     setCurrentChannel(channelId);

packages/web/src/components/layout/MainContent.tsx

@@ -72,7 +72,7 @@ export function MainContent() {
 
   // 2. LOGIC AND EARLY RETURNS
   const channel = channels.find(c => c.id === currentChannelId);
-  const isVoiceChannel = channel?.type === 'voice' || channel?.type === 'video';
+  const isVoiceChannel = channel?.type === 'voice';
 
   if (showDms || isExplorePage || !currentSpaceId) {
     if (!currentChannelId) {