fix(db): add CREATE EXTENSION vector before first migration using pgvector

The insights table uses vector(1536) but no migration enables the pgvector
extension. CI postgres (pgvector/pgvector:pg17) has the extension available
but it must be explicitly created before use.

Adds CREATE EXTENSION IF NOT EXISTS vector at the top of
0001_cynical_ultimatum.sql (the first migration referencing vector type).

packages/db/drizzle/0001_cynical_ultimatum.sql

@@ -1,3 +1,4 @@
+CREATE EXTENSION IF NOT EXISTS vector;--> statement-breakpoint
 CREATE TABLE "agent_logs" (
 	"id" uuid PRIMARY KEY DEFAULT gen_random_uuid() NOT NULL,
 	"session_id" text NOT NULL,