feat: persist research conversations and refine deck headers

drizzle/0003_romantic_scrambler.sql

@@ -0,0 +1,14 @@
+CREATE TABLE `research_sessions` (
+	`id` text PRIMARY KEY NOT NULL,
+	`title` text NOT NULL,
+	`status` text NOT NULL,
+	`updated_at` integer NOT NULL,
+	`snapshot` text NOT NULL
+);
+--> statement-breakpoint
+CREATE TABLE `research_state` (
+	`id` integer PRIMARY KEY NOT NULL,
+	`active_session_id` text,
+	FOREIGN KEY (`active_session_id`) REFERENCES `research_sessions`(`id`) ON UPDATE no action ON DELETE set null,
+	CONSTRAINT "research_state_singleton" CHECK("research_state"."id" = 1)
+);