feat: add agent search config and system assistant defaults

Adds a config jsonb column to agents for per-agent search settings
(enabled, rerank, maxResults). Types systemAssistants with rename and
rerank sub-objects. Backfills missing systemAssistants keys on settings
fetch. Includes generated drizzle migrations.

drizzle/schema.ts

@@ -23,7 +23,16 @@ export enum ToolCallType {
 export const settings = pgTable('settings', {
     id: text('id').primaryKey().$defaultFn(nanoid),
     userId: text('user_id').notNull(),
-    systemAssistants: jsonb('system_assistants').$type<Record<string, any>>().notNull().default({}),
+    systemAssistants: jsonb('system_assistants').$type<{
+        rename: {
+            enabled: boolean;
+            modelId: string | null;
+        };
+        rerank: {
+            enabled: boolean;
+            modelId: string | null;
+        };
+    }>().notNull().default({} as any),
     appearance: jsonb('appearance').$type<{
         colorScheme?: 'light' | 'dark' | 'system';
         accent?: string;
@@ -93,6 +102,13 @@ export const agents = pgTable('agents', {
     systemPrompt: text('system_prompt'),
     imageUrl: text('image_url'),
     defaultModelId: text('default_model_id').references(() => models.id, { onDelete: 'set null' }),
+    config: jsonb('config').$type<{
+        search?: {
+            enabled: boolean;
+            rerank: boolean;
+            maxResults: number;
+        }
+    }>().default({}),
     createdAt: timestamp('created_at').notNull().defaultNow(),
 }, (table) => [
     index('agents_userId_idx').on(table.userId),
@@ -215,7 +231,7 @@ export const embeddings = pgTable('embeddings', {
 export const attachments = pgTable('attachments', {
     id: text('id').primaryKey().$defaultFn(nanoid),
     userId: text('user_id').notNull(),
-    topicId: text('topic_id').notNull().references(() => topics.id),
+    topicId: text('topic_id').notNull().references(() => topics.id, { onDelete: 'cascade' }),
     messageId: text('message_id').notNull().references(() => messages.id, { onDelete: 'cascade' }),
     fileId: text('file_id').notNull().references(() => files.id, { onDelete: 'cascade' }),
     createdAt: timestamp('created_at').notNull().defaultNow(),