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/routes/discovery.test.ts

@@ -40,7 +40,7 @@ async function insertPublicSetup(
 ) {
 	const [row] = await db
 		.insert(setups)
-		.values({ name, userId, isPublic: true })
+		.values({ name, userId, visibility: "public" })
 		.returning();
 	return row;
 }
@@ -76,7 +76,7 @@ describe("Discovery Routes", () => {
 			// Insert a private setup
 			await db
 				.insert(setups)
-				.values({ name: "Private Setup", userId, isPublic: false });
+				.values({ name: "Private Setup", userId, visibility: "private" });
 
 			const res = await app.request("/api/discovery/setups");
 			expect(res.status).toBe(200);