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>

drizzle-pg/meta/_journal.json

@@ -36,6 +36,13 @@
       "when": 1776016552627,
       "tag": "0004_smiling_night_nurse",
       "breakpoints": true
+    },
+    {
+      "idx": 5,
+      "version": "7",
+      "when": 1776095449827,
+      "tag": "0005_true_green_goblin",
+      "breakpoints": true
     }
   ]
 }