fix: replace global email UNIQUE with partial index scoped to role=user

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01LP9Q4kfCAYAjJnsbHBrViZ

db/migrations/011_users_email_partial_unique.sql

@@ -0,0 +1,30 @@
+-- Migration: replace global email UNIQUE with partial index (hosting accounts only)
+-- Allows admin/reseller emails to be reused for hosting accounts
+CREATE TABLE IF NOT EXISTS users_new (
+  id            INTEGER PRIMARY KEY AUTOINCREMENT,
+  username      TEXT NOT NULL UNIQUE,
+  password      TEXT NOT NULL,
+  email         TEXT NOT NULL,
+  role          TEXT NOT NULL DEFAULT 'user' CHECK(role IN ('admin','reseller','user')),
+  status        TEXT NOT NULL DEFAULT 'active' CHECK(status IN ('active','suspended','pending')),
+  reseller_id   INTEGER DEFAULT NULL,
+  package_id    INTEGER DEFAULT NULL,
+  theme         TEXT DEFAULT 'nova-dark',
+  language      TEXT DEFAULT 'en',
+  contact_name  TEXT,
+  contact_phone TEXT,
+  last_login    TEXT,
+  created_at    TEXT DEFAULT (datetime('now')),
+  updated_at    TEXT,
+  totp_secret   TEXT,
+  totp_enabled  INTEGER DEFAULT 0,
+  totp_backup_codes TEXT,
+  FOREIGN KEY (reseller_id) REFERENCES users(id) ON DELETE SET NULL
+);
+INSERT OR IGNORE INTO users_new SELECT id,username,password,email,role,status,reseller_id,package_id,theme,language,contact_name,contact_phone,last_login,created_at,updated_at,totp_secret,totp_enabled,totp_backup_codes FROM users;
+DROP TABLE users;
+ALTER TABLE users_new RENAME TO users;
+CREATE INDEX IF NOT EXISTS idx_users_role     ON users (role);
+CREATE INDEX IF NOT EXISTS idx_users_status   ON users (status);
+CREATE INDEX IF NOT EXISTS idx_users_reseller ON users (reseller_id);
+CREATE UNIQUE INDEX IF NOT EXISTS idx_users_email_user ON users (email) WHERE role = 'user';