Add MariaDB integration and repositories

Introduce DB support and repos: add modules/database.js (connection pool + runDDL) and SQL DDL files (data/ddl/*) for servers, users, providers, identities and credentials. Add repository layers: users, servers, providers, identities, credentials. Update server.js to run DDL at startup. Update .env.example with DB settings and bump dependencies in package.json/package-lock.json (add mariadb, bump dotenv/helmet/path-to-regexp/zod and dev tool upgrades). Error handling and logging included for DDL and repo operations.

repositories/serversRepo.js

@@ -0,0 +1,78 @@
+const { pool } = require("../modules/database")
+const { DefaultError } = require("../errors/errors")
+
+async function findById(id) {
+    try {
+        const sql = "SELECT* FROM servers WHERE id = ?"
+        const rows = await pool.query(sql, [id])
+        return rows[0] || null
+    } catch (error) {
+        throw new DefaultError(500, "Internal Server Error", error)
+    }
+}
+
+async function findByUrl(url) {
+    try {
+        const sql = "SELECT* FROM servers WHERE url = ?"
+        const rows = await pool.query(sql, [url])
+        return rows[0] || null
+    } catch (error) {
+        throw new DefaultError(500, "Internal Server Error", error)
+    }
+}
+
+async function create(url, publicKey) {
+    try {
+        const sql = "INSERT INTO servers (serverUrl, publicKey) VALUES (?, ?)"
+        const rows = await pool.query(sql, [url, publicKey])
+        return rows[0] || null
+    } catch (error) {
+        throw new DefaultError(500, "Internal Server Error", error)
+    }
+}
+
+async function remove(id) {
+    try {
+        const sql = "DELETE FROM servers WHERE id = ?"
+        const rows = await pool.query(sql, [id])
+        return rows.affectedRows > 0
+    } catch (error) {
+        throw new DefaultError(500, "Internal Server Error", error)
+    }
+}
+
+async function updateServer(id, serverUrl, publicKey) {
+    try {
+        const fields = []
+        const params = { id }
+
+        if (serverUrl !== undefined) {
+            fields.push('`serverUrl` = :serverUrl')
+            params.serverUrl = serverUrl
+        }
+
+        if (publicKey !== undefined) {
+            fields.push('`publicKey` = :publicKey')
+            params.publicKey = publicKey
+        }
+
+        if (fields.length === 0) {
+            return findById(id)
+        }
+
+        const sql = `UPDATE servers SET ${fields.join(', ')} WHERE id = :id`
+        await pool.query(sql, params)
+
+        return findById(id)
+    } catch (error) {
+        throw new DefaultError(500, "Internal Server Error", error)
+    }
+}
+
+module.exports = {
+    create,
+    remove,
+    findById,
+    findByUrl,
+    updateServer
+}