Prepare secure config and reliable workout sync

backend/Config.php

@@ -0,0 +1,84 @@
+<?php
+/**
+ * Reads server-side application configuration without bundling secrets.
+ * The deploy layout places a .env symlink beside backend/, outside public/.
+ */
+final class AppConfig
+{
+    private static $loaded = false;
+
+    public static function loadEnvironment()
+    {
+        if (self::$loaded) {
+            return;
+        }
+
+        $path = getenv('APP_ENV_FILE');
+        if ($path === false || $path === '') {
+            $path = dirname(__DIR__) . DIRECTORY_SEPARATOR . '.env';
+        }
+
+        if (!is_file($path) || !is_readable($path)) {
+            throw new RuntimeException('Server environment file is missing or unreadable');
+        }
+
+        $lines = file($path, FILE_IGNORE_NEW_LINES);
+        if ($lines === false) {
+            throw new RuntimeException('Unable to read server environment file');
+        }
+
+        foreach ($lines as $lineNumber => $line) {
+            $line = trim($line);
+            if ($line === '' || $line[0] === '#') {
+                continue;
+            }
+
+            if (!preg_match('/^([A-Z][A-Z0-9_]*)\s*=\s*(.*)$/', $line, $matches)) {
+                throw new RuntimeException('Invalid environment entry on line ' . ($lineNumber + 1));
+            }
+
+            $name = $matches[1];
+            $value = trim($matches[2]);
+            if (strlen($value) >= 2) {
+                $first = $value[0];
+                $last = substr($value, -1);
+                if (($first === '"' && $last === '"') || ($first === "'" && $last === "'")) {
+                    $value = substr($value, 1, -1);
+                }
+            }
+
+            // Explicit process environment values override the file.
+            if (getenv($name) === false) {
+                putenv($name . '=' . $value);
+                $_ENV[$name] = $value;
+            }
+        }
+
+        self::$loaded = true;
+    }
+
+    public static function required($name)
+    {
+        self::loadEnvironment();
+        $value = getenv($name);
+        if ($value === false || $value === '') {
+            throw new RuntimeException('Required server setting is missing: ' . $name);
+        }
+        return $value;
+    }
+
+    public static function integer($name, $default)
+    {
+        self::loadEnvironment();
+        $value = getenv($name);
+        if ($value === false || $value === '') {
+            return (int) $default;
+        }
+
+        $parsed = filter_var($value, FILTER_VALIDATE_INT);
+        if ($parsed === false) {
+            throw new RuntimeException('Server setting must be an integer: ' . $name);
+        }
+        return $parsed;
+    }
+}