docs/refactor: rename getModuleMetadata and update route auth format

- Rename `getModuleMetadata` to `getModuleMetadataGenerator` in registry,
  index, and client exports to clarify its purpose (returns a generator
  function, not a metadata object)
- Add new `getModuleMetadata` and `getMetadataGenerator` exports from
  `modules.metadata.js` for server-side metadata object retrieval
- Update route auth format in docs from `requireAuth`/`requireAdmin`
  flags to a single `auth` field with values: `'admin'`, `'user'`,
  or `'public'`
- Fix `isModuleEnabledInEnv` to replace hyphens with underscores in
  env var names (e.g. `my-module` → `ZEN_MODULE_MY_MODULE`)
- Replace `useState` initializer in `ZenProvider` with `useRef` guard
  to avoid React strict mode double-invocation issues

src/modules/modules.actions.js

@@ -9,7 +9,7 @@
  *   const { getInvoiceByToken } = getModuleActions('invoice');
  */
 
-import { getModule } from '../core/modules/registry.js';
+import { getModule, getEnabledModules } from '../core/modules/registry.js';
 
 // Static actions for internal modules (add entries here for new internal modules)
 export const MODULE_ACTIONS = {
@@ -43,14 +43,15 @@ export function getModuleDashboardAction(moduleName) {
 }
 
 /**
- * Get all dashboard stats from all modules
+ * Get all dashboard stats from all modules (internal static + external runtime).
  * @returns {Promise<Object>} Object with module names as keys and stats as values
  */
 export async function getAllModuleDashboardStats() {
   const stats = {};
 
+  // Internal modules — static action map
   for (const [moduleName, getStats] of Object.entries(MODULE_DASHBOARD_ACTIONS)) {
-    const envKey = `ZEN_MODULE_${moduleName.toUpperCase()}`;
+    const envKey = `ZEN_MODULE_${moduleName.toUpperCase().replace(/-/g, '_')}`;
     if (process.env[envKey] !== 'true') continue;
 
     try {
@@ -63,6 +64,20 @@ export async function getAllModuleDashboardStats() {
     }
   }
 
+  // External modules — runtime registry
+  for (const mod of getEnabledModules()) {
+    if (mod.external && typeof mod.actions?.getDashboardStats === 'function') {
+      try {
+        const result = await mod.actions.getDashboardStats();
+        if (result.success) {
+          stats[mod.name] = result.stats;
+        }
+      } catch (error) {
+        console.error(`Error getting dashboard stats for ${mod.name}:`, error);
+      }
+    }
+  }
+
   return stats;
 }