feat: migrate setup visibility from boolean to three-tier system

Replace isPublic boolean with visibility enum (private/link/public) across
the full stack. Add shares table to schema for future share link support.
Update all services, routes, schemas, hooks, components, and tests.

Plan: 32-01 (Setup Sharing System - Schema Migration)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

tests/services/discovery.service.test.ts

@@ -47,7 +47,7 @@ async function insertPublicSetup(
 ) {
 	const [setup] = await db
 		.insert(setups)
-		.values({ name, userId, isPublic: true })
+		.values({ name, userId, visibility: "public" })
 		.returning();
 	for (const itemId of itemIds) {
 		await db.insert(setupItems).values({ setupId: setup.id, itemId });
@@ -62,7 +62,7 @@ async function insertPrivateSetup(
 ) {
 	const [setup] = await db
 		.insert(setups)
-		.values({ name, userId, isPublic: false })
+		.values({ name, userId, visibility: "private" })
 		.returning();
 	return setup;
 }