docs: Day 12-13 completion summary and milestone update

backend/prisma/migrations/20251010122727_add_conversation_metadata_deleted_at/migration.sql

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+/*
+  Warnings:
+
+  - You are about to drop the column `description` on the `projects` table. All the data in the column will be lost.
+
+*/
+-- AlterTable
+ALTER TABLE "conversations" ADD COLUMN     "deleted_at" TIMESTAMP(3),
+ADD COLUMN     "metadata" JSONB;
+
+-- AlterTable
+ALTER TABLE "messages" ADD COLUMN     "model" TEXT;
+
+-- AlterTable
+ALTER TABLE "projects" DROP COLUMN "description",
+ADD COLUMN     "background" TEXT NOT NULL DEFAULT '',
+ADD COLUMN     "deleted_at" TIMESTAMP(3),
+ADD COLUMN     "research_type" TEXT NOT NULL DEFAULT 'observational';
+
+-- CreateIndex
+CREATE INDEX "conversations_deleted_at_idx" ON "conversations"("deleted_at");
+
+-- CreateIndex
+CREATE INDEX "projects_deleted_at_idx" ON "projects"("deleted_at");