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.

.env.example

@@ -15,15 +15,26 @@ ZEN_DATABASE_URL=postgres://USER:PASSWORD@HOST:PORT/postgres
 ZEN_DATABASE_URL_DEV=postgres://USER:PASSWORD@HOST:PORT/postgres_dev
 ZEN_DB_SSL_DISABLED=false
 
-# STORAGE (S3-compatible — Cloudflare R2 ou Backblaze B2)
-# R2 : ZEN_STORAGE_ENDPOINT=<accountId>.r2.cloudflarestorage.com  ZEN_STORAGE_REGION=auto
-# B2 : ZEN_STORAGE_ENDPOINT=s3.<region>.backblazeb2.com            ZEN_STORAGE_REGION=<region>
+# STORAGE
+# Fournisseur : 'r2' (défaut) ou 'backblaze'
+ZEN_STORAGE_PROVIDER=r2
+
+# Cloudflare R2 (ZEN_STORAGE_PROVIDER=r2)
+# Endpoint format : <accountId>.r2.cloudflarestorage.com
 ZEN_STORAGE_ENDPOINT=
 ZEN_STORAGE_REGION=auto
 ZEN_STORAGE_BUCKET=
 ZEN_STORAGE_ACCESS_KEY=
 ZEN_STORAGE_SECRET_KEY=
 
+# Backblaze B2 (ZEN_STORAGE_PROVIDER=backblaze)
+# Endpoint format : s3.<region>.backblazeb2.com
+ZEN_STORAGE_B2_ENDPOINT=
+ZEN_STORAGE_B2_REGION=
+ZEN_STORAGE_B2_BUCKET=
+ZEN_STORAGE_B2_ACCESS_KEY=
+ZEN_STORAGE_B2_SECRET_KEY=
+
 # EMAIL
 ZEN_EMAIL_RESEND_APIKEY=
 ZEN_EMAIL_FROM_NAME="EXEMPLE"