fix: DM close visibility flag, wire Remove Friend button, harden deploy script

- Redesign DM close as a visibility flag (closed column) instead of row deletion,
  so message broadcasts still reach users who closed a DM conversation
- Add broadcastDmMessage() helper that auto-resurfaces closed DMs when new messages arrive
- Wire Remove Friend button in DM welcome header with onClick handler and friend check
- Fix deploy.sh to cd to its own directory so rsync always runs from project root

packages/server/src/db/migrate.ts

@@ -35,6 +35,12 @@ export function runMigrations(db: Database.Database): void {
       columns: [
         { name: 'dm_message_id', type: 'TEXT' }
       ]
+    },
+    {
+      name: 'dm_members',
+      columns: [
+        { name: 'closed', type: 'INTEGER DEFAULT 0' }
+      ]
     }
   ];