fix(storage): route every file op through getStorageBackend()

Removes 12 direct minioClient.{put,get,remove}Object call sites that
bypassed the pluggable storage abstraction.  Filesystem-mode deploys
(MULTI_NODE_DEPLOYMENT=false, storage_backend=filesystem) silently
broke at every site: GDPR export, invoice PDF, EOI generation, portal
download, file upload, folder create/rename/delete, signed PDF land,
maintenance cleanup, etc.  Each site now resolves the active backend
and uses its put/get/delete + the new presignDownloadUrl() helper.

Folder marker objects in /files/folders/* keep the same on-the-wire
shape but route through the backend.  A future refactor should move
folder bookkeeping to a DB-backed virtual-folder table (see audit
HIGH §3 follow-up note in the route file).

Sites left untouched: src/lib/services/system-monitoring.service.ts
and src/app/api/ready/route.ts use minioClient.bucketExists as an S3-
specific health probe — those are correctly mode-aware and stay.

Refs: docs/audit-comprehensive-2026-05-05.md HIGH §3 (auditor-D Issue 1)

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/lib/services/email-compose.service.ts

@@ -114,8 +114,8 @@ export async function sendEmail(
             where: eq(files.id, ref.fileId),
           });
           if (!file) throw new NotFoundError('File');
-          const { minioClient } = await import('@/lib/minio');
-          const stream = await minioClient.getObject(file.storageBucket, file.storagePath);
+          const { getStorageBackend } = await import('@/lib/storage');
+          const stream = await (await getStorageBackend()).get(file.storagePath);
           const chunks: Buffer[] = [];
           for await (const chunk of stream) {
             chunks.push(Buffer.isBuffer(chunk) ? chunk : Buffer.from(chunk));