feat(storage): refactor storage config and remove module registry

Introduce a dedicated `storage-config.js` for registering public
prefixes and access policies via `configureStorageApi()`, replacing the
previous `getAllStoragePublicPrefixes` / `getAllStorageAccessPolicies`
imports from the module registry.

Remove `getAllApiRoutes()` from the router so module-level routes are no
longer auto-collected; feature routes must now be registered explicitly
via `registerFeatureRoutes()` during `initializeZen()`.

Update `.env.example` to document separate `ZEN_STORAGE_PROVIDER`,
`ZEN_STORAGE_B2_*` variables for Backblaze B2 alongside the existing
Cloudflare R2 variables, making provider selection explicit.

Clean up admin navigation and page components to drop module-injected
nav entries, keeping only core and system sections.

src/features/admin/navigation.server.js

@@ -15,20 +15,12 @@
  * Icons are passed as string names and resolved on the client.
  */
 
-// Import from the main package to use the same registry as discovery
-import { moduleSystem } from '@zen/core';
-const { getAllAdminNavigation } = moduleSystem;
-
 /**
- * Build complete navigation sections including modules
- * This should ONLY be called on the server (in page.js)
+ * Build complete navigation sections
  * @param {string} pathname - Current pathname
- * @param {Object} enabledModules - Object with module names as keys (for compatibility)
  * @returns {Array} Complete navigation sections (serializable, icons as strings)
  */
-export function buildNavigationSections(pathname, enabledModules = null) {
-  // Core navigation sections (always available)
-  // Use icon NAMES (strings) for serialization across server/client boundary
+export function buildNavigationSections(pathname) {
   const coreNavigation = [
     {
       id: 'Dashboard',
@@ -45,10 +37,6 @@ export function buildNavigationSections(pathname, enabledModules = null) {
     }
   ];
   
-  // Get module navigation from registry (only works on server)
-  const moduleNavigation = getAllAdminNavigation(pathname);
-  
-  // System navigation (always at the end)
   const systemNavigation = [
     {
       id: 'users',
@@ -65,5 +53,5 @@ export function buildNavigationSections(pathname, enabledModules = null) {
     }
   ];
   
-  return [...coreNavigation, ...moduleNavigation, ...systemNavigation];
+  return [...coreNavigation, ...systemNavigation];
 }