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/index.js

@@ -23,20 +23,11 @@ export * as stripe from "./core/payments/stripe.js";
 // Export PDF utilities as namespace
 export * as pdf from "./core/pdf/index.js";
 
-// Export module system as namespace
-export * as moduleSystem from "./core/modules/index.js";
-
 // NOTE: Toast components are CLIENT ONLY - import from '@zen/core/toast'
 // Do not export here to avoid mixing client/server boundaries
 
-// Export modules system as namespace (legacy, includes invoice module)
-export * as modules from "./modules/index.js";
-
-// Export public pages (Zen routes)
-export { PublicPagesLayout, PublicPagesClient } from "./modules/pages.js";
-
 // Export app configuration utilities
-export { getAppName, getAppConfig, getSessionCookieName, getModulesConfig, getPublicBaseUrl } from "./shared/lib/appConfig.js";
+export { getAppName, getAppConfig, getSessionCookieName, getPublicBaseUrl } from "./shared/lib/appConfig.js";
 
 // Export initialization utilities
 export { initializeZen, resetZenInitialization } from "./shared/lib/init.js";