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-data.ts

@@ -857,7 +857,7 @@ export const DEV_THREADS = [
 export const DEV_SETUPS = [
 	{
 		name: "Weekend Overnighter",
-		isPublic: true,
+		visibility: "public" as const,
 		items: [
 			{ userItemIndex: 0, classification: "base" }, // Terrapin saddle bag
 			{ userItemIndex: 3, classification: "base" }, // X-Mid 1
@@ -871,7 +871,7 @@ export const DEV_SETUPS = [
 	},
 	{
 		name: "Ultra-Light Day Ride",
-		isPublic: false,
+		visibility: "private" as const,
 		items: [
 			{ userItemIndex: 2, classification: "base" }, // Top tube pack
 			{ userItemIndex: 7, classification: "worn" }, // Nitecore NU25