Add PostgreSQL, user/squad management, remove private domains from docs

internal/db/migrations/001_init.sql

@@ -0,0 +1,29 @@
+CREATE TABLE IF NOT EXISTS telegram_users (
+    id BIGSERIAL PRIMARY KEY,
+    telegram_id BIGINT NOT NULL UNIQUE,
+    username TEXT,
+    first_name TEXT,
+    created_at TIMESTAMPTZ NOT NULL DEFAULT NOW()
+);
+
+CREATE TABLE IF NOT EXISTS vpn_users (
+    id BIGSERIAL PRIMARY KEY,
+    telegram_id BIGINT,
+    remnawave_uuid UUID NOT NULL UNIQUE,
+    remnawave_username VARCHAR(36) NOT NULL,
+    external_squad_uuid UUID,
+    internal_squad_uuids UUID[] NOT NULL DEFAULT '{}',
+    expire_at TIMESTAMPTZ,
+    created_at TIMESTAMPTZ NOT NULL DEFAULT NOW(),
+    updated_at TIMESTAMPTZ NOT NULL DEFAULT NOW()
+);
+
+CREATE INDEX IF NOT EXISTS idx_vpn_users_telegram ON vpn_users(telegram_id);
+CREATE INDEX IF NOT EXISTS idx_vpn_users_username ON vpn_users(remnawave_username);
+
+CREATE TABLE IF NOT EXISTS admin_wizard (
+    admin_telegram_id BIGINT PRIMARY KEY,
+    step TEXT NOT NULL,
+    data JSONB NOT NULL DEFAULT '{}',
+    updated_at TIMESTAMPTZ NOT NULL DEFAULT NOW()
+);