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

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}`);

src/db/schema.ts

@@ -1,5 +1,4 @@
 import {
-	boolean,
 	doublePrecision,
 	integer,
 	pgTable,
@@ -121,7 +120,7 @@ export const setups = pgTable("setups", {
 	userId: integer("user_id")
 		.notNull()
 		.references(() => users.id),
-	isPublic: boolean("is_public").notNull().default(false),
+	visibility: text("visibility").notNull().default("private"),
 	createdAt: timestamp("created_at").defaultNow().notNull(),
 	updatedAt: timestamp("updated_at").defaultNow().notNull(),
 });
@@ -139,6 +138,21 @@ export const setupItems = pgTable("setup_items", {
 	classification: text("classification").notNull().default("base"),
 });
 
+// ── Shares ─────────────────────────────────────────────────────────
+
+export const shares = pgTable("shares", {
+	id: serial("id").primaryKey(),
+	setupId: integer("setup_id")
+		.notNull()
+		.references(() => setups.id, { onDelete: "cascade" }),
+	token: text("token").notNull().unique(),
+	permission: text("permission").notNull().default("read"),
+	expiresAt: timestamp("expires_at"),
+	userId: integer("user_id").references(() => users.id),
+	createdAt: timestamp("created_at").defaultNow().notNull(),
+	revokedAt: timestamp("revoked_at"),
+});
+
 // ── Global Items ────────────────────────────────────────────────────
 
 export const globalItems = pgTable(