feat: support concurrent Reddit accounts

tests/database.test.ts

@@ -106,8 +106,8 @@ describe('Database Client', () => {
       const tables = db
         .prepare("SELECT name FROM sqlite_master WHERE type='table' AND name NOT LIKE 'sqlite_%'")
         .all() as { name: string }[];
-      // Eight domain tables plus the singleton application configuration table.
-      expect(tables.length).toBe(9);
+      // Existing domain/config tables plus account, conversation, sync and media ownership stores.
+      expect(tables.length).toBe(13);
     });
 
     it('tracks schema version and migrates a legacy sent_messages table transactionally', () => {
@@ -138,7 +138,8 @@ describe('Database Client', () => {
       const columns = db.prepare('PRAGMA table_info(processed_posts)').all() as { name: string; notnull: number }[];
       const columnMap = new Map(columns.map(c => [c.name, c]));
 
-      expect(columnMap.get('id')?.notnull).toBe(0); // TEXT is not NOT NULL by default
+      expect(columnMap.get('account_id')?.notnull).toBe(1);
+      expect(columnMap.get('id')?.notnull).toBe(1); // Composite account-scoped primary key
       expect(columnMap.get('subreddit')?.notnull).toBe(1);
       expect(columnMap.get('author')?.notnull).toBe(1);
       expect(columnMap.get('title')?.notnull).toBe(1);