Add subdirectory routing mode for public domain deployments

Apps can now be served at domain.com/appname/ instead of requiring
subdomain DNS records (appname.domain.com). Supports three subpath
modes per template: native (URL base env var), strip (handle_path),
and none (incompatible warning). Tested on Linux with deploy/removal
lifecycle verified.

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

dashcaddy-api/config-schema.js

@@ -93,13 +93,31 @@ function validateConfig(config) {
     }
   }
 
+  // Routing mode validation
+  if (config.routingMode !== undefined) {
+    const validModes = ['subdomain', 'subdirectory'];
+    if (!validModes.includes(config.routingMode)) {
+      errors.push(`routingMode "${config.routingMode}" is not one of: ${validModes.join(', ')}`);
+    }
+  }
+
+  // Domain validation
+  if (config.domain !== undefined) {
+    if (typeof config.domain !== 'string') {
+      errors.push('domain must be a string');
+    } else if (config.domain && !/^[a-z0-9][a-z0-9.-]*\.[a-z]{2,}$/i.test(config.domain)) {
+      warnings.push(`domain "${config.domain}" may not be a valid domain name`);
+    }
+  }
+
   // Warn on unknown top-level keys
   const knownKeys = [
     'tld', 'caName', 'dns', 'dnsServers', 'dashboardHost', 'timezone', 'theme',
     'updatedAt', 'timestamp', 'logo', 'logoPosition', 'favicon', 'weather',
     'setupComplete', 'setupCompleted', 'setupMode', 'onboardingCompleted',
     'configurationType', 'defaults', 'customLogo', 'customFavicon',
-    'dashboardTitle', 'tailscale', 'license', 'skipped'
+    'dashboardTitle', 'tailscale', 'license', 'skipped',
+    'routingMode', 'domain', 'email', 'defaultIP'
   ];
   for (const key of Object.keys(config)) {
     if (!knownKeys.includes(key)) {