feat(18-02): implement global item service, seed script, and seed integration

- searchGlobalItems with LIKE-based case-insensitive search and wildcard escaping
- getGlobalItemWithOwnerCount with owner count from junction table
- linkItemToGlobal/unlinkItemFromGlobal for item-global linking
- seedGlobalItems idempotent seed from JSON catalog
- Integrated seed into seedDefaults startup

src/db/seed-global-items.ts

@@ -0,0 +1,27 @@
+import { db as prodDb } from "./index.ts";
+import { globalItems } from "./schema.ts";
+import seedData from "./global-items-seed.json";
+
+type Db = typeof prodDb;
+
+/**
+ * Seed the global items table with initial bikepacking gear data.
+ * Idempotent: skips if any rows already exist.
+ */
+export function seedGlobalItems(db: Db = prodDb) {
+	const existing = db.select().from(globalItems).limit(1).all();
+	if (existing.length > 0) return;
+
+	for (const item of seedData) {
+		db.insert(globalItems)
+			.values({
+				brand: item.brand,
+				model: item.model,
+				category: item.category ?? null,
+				weightGrams: item.weightGrams ?? null,
+				priceCents: item.priceCents ?? null,
+				description: item.description ?? null,
+			})
+			.run();
+	}
+}