feat: per-user assistant name and system prompt customization

Each user can rename the AI assistant and edit their own system prompt in Settings.

drizzle/0024_user_assistant_customization.sql

@@ -0,0 +1,2 @@
+ALTER TABLE "users" ADD COLUMN "assistant_name" text DEFAULT 'Assistant' NOT NULL;--> statement-breakpoint
+ALTER TABLE "users" ADD COLUMN "assistant_system_prompt" text;

drizzle/meta/_journal.json

@@ -169,6 +169,13 @@
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       "tag": "0023_comments",
       "breakpoints": true
+    },
+    {
+      "idx": 24,
+      "version": "7",
+      "when": 1780394000000,
+      "tag": "0024_user_assistant_customization",
+      "breakpoints": true
     }
   ]
 }