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/shared/schemas.ts

@@ -85,12 +85,15 @@ export const reorderCandidatesSchema = z.object({
 // Setup schemas
 export const createSetupSchema = z.object({
 	name: z.string().min(1, "Setup name is required"),
-	isPublic: z.boolean().optional().default(false),
+	visibility: z
+		.enum(["private", "link", "public"])
+		.optional()
+		.default("private"),
 });
 
 export const updateSetupSchema = z.object({
 	name: z.string().min(1, "Setup name is required"),
-	isPublic: z.boolean().optional(),
+	visibility: z.enum(["private", "link", "public"]).optional(),
 });
 
 export const syncSetupItemsSchema = z.object({