feat(19-01): update schema with reference item model and tags tables

- Add globalItemId and purchasePriceCents columns to items table
- Add globalItemId column to threadCandidates table
- Add tags and globalItemTags tables for tag system
- Remove itemGlobalLinks table (replaced by direct FK)
- Generate migration with data migration step before table drop

src/db/schema.ts

@@ -55,6 +55,8 @@ export const items = pgTable("items", {
 	imageFilename: text("image_filename"),
 	imageSourceUrl: text("image_source_url"),
 	quantity: integer("quantity").notNull().default(1),
+	globalItemId: integer("global_item_id").references(() => globalItems.id),
+	purchasePriceCents: integer("purchase_price_cents"),
 	createdAt: timestamp("created_at").defaultNow().notNull(),
 	updatedAt: timestamp("updated_at").defaultNow().notNull(),
 });
@@ -97,6 +99,7 @@ export const threadCandidates = pgTable("thread_candidates", {
 	pros: text("pros"),
 	cons: text("cons"),
 	sortOrder: doublePrecision("sort_order").notNull().default(0),
+	globalItemId: integer("global_item_id").references(() => globalItems.id),
 	createdAt: timestamp("created_at").defaultNow().notNull(),
 	updatedAt: timestamp("updated_at").defaultNow().notNull(),
 });
@@ -141,19 +144,29 @@ export const globalItems = pgTable("global_items", {
 	createdAt: timestamp("created_at").defaultNow().notNull(),
 });
 
-// ── Item Global Links ───────────────────────────────────────────────
+// ── Tags ───────────────────────────────────────────────────────────
 
-export const itemGlobalLinks = pgTable("item_global_links", {
+export const tags = pgTable("tags", {
 	id: serial("id").primaryKey(),
-	itemId: integer("item_id")
-		.notNull()
-		.references(() => items.id, { onDelete: "cascade" })
-		.unique(),
-	globalItemId: integer("global_item_id")
-		.notNull()
-		.references(() => globalItems.id, { onDelete: "cascade" }),
+	name: text("name").notNull().unique(),
+	createdAt: timestamp("created_at").defaultNow().notNull(),
 });
 
+// ── Global Item Tags ───────────────────────────────────────────────
+
+export const globalItemTags = pgTable(
+	"global_item_tags",
+	{
+		globalItemId: integer("global_item_id")
+			.notNull()
+			.references(() => globalItems.id, { onDelete: "cascade" }),
+		tagId: integer("tag_id")
+			.notNull()
+			.references(() => tags.id, { onDelete: "cascade" }),
+	},
+	(table) => [primaryKey({ columns: [table.globalItemId, table.tagId] })],
+);
+
 // ── Settings ────────────────────────────────────────────────────────
 
 export const settings = pgTable(