Fix multiple user panel 500 errors

- domains: VhostManager::create() called with array instead of 4 params
- PHPManager: VhostManager not required; pool writes use sudo tee (permission);
  updateConfig creates pool if missing instead of throwing
- DatabaseManager: MySQL ops used SQLite panel PDO; add dedicated mysqlPdo()
  using MariaDB socket auth
- BackupManager: column name is size_mb not size; diskUsage returns float
- DB.php: add LAST_INSERT_ID() → last_insert_rowid() translation
- user.js: SSL issue/submit used Nova.api (JSON) but endpoint streams SSE;
  add _sslStream() helper matching admin panel behavior
- schema/migration: add enc_password column to email_accounts

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

db/migrations/010_email_enc_password.sql

@@ -0,0 +1 @@
+ALTER TABLE email_accounts ADD COLUMN enc_password TEXT;

db/schema.sql

@@ -183,9 +183,10 @@ CREATE INDEX IF NOT EXISTS idx_dns_records_type ON dns_records (type);
 CREATE TABLE IF NOT EXISTS email_accounts (
   id         INTEGER PRIMARY KEY AUTOINCREMENT,
   account_id INTEGER NOT NULL,
-  email      TEXT NOT NULL UNIQUE,
-  password   TEXT NOT NULL,
-  quota_mb   INTEGER DEFAULT 500,
+  email        TEXT NOT NULL UNIQUE,
+  password     TEXT NOT NULL,
+  enc_password TEXT,
+  quota_mb     INTEGER DEFAULT 500,
   used_mb    INTEGER DEFAULT 0,
   status     TEXT DEFAULT 'active' CHECK(status IN ('active','suspended')),
   created_at TEXT DEFAULT (datetime('now')),