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>

src/db/dev-seed.ts

@@ -252,7 +252,7 @@ async function seedDevData(database: Db = db) {
 				.values({
 					name: setupDef.name,
 					userId,
-					isPublic: setupDef.isPublic,
+					visibility: setupDef.visibility,
 				})
 				.returning();
 			if (!setup) throw new Error(`Failed to insert setup: ${setupDef.name}`);