Add file module for uploads and storage

- File model + migration: file metadata, content lives in object storage
- IFileStorage port with local disk and S3-compatible (RustFS/MinIO) adapters
- POST /files, GET /files/:id/download, DELETE /files/:id
- MIME sniffed from content; only safe images served inline, nosniff header
- FileOwnerRegistry: owner modules register to grant visibility and keep
  their files from GC; FileGcService removes orphaned files hourly
- TransformResponseInterceptor passes StreamableFile through

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

package.json

@@ -24,6 +24,7 @@
   "dependencies": {
     "@apollo/server": "^5.5.1",
     "@as-integrations/express5": "^1.1.2",
+    "@aws-sdk/client-s3": "^3.1145.0",
     "@better-auth/prisma-adapter": "^1.7.2",
     "@nestjs/apollo": "^14.0.0",
     "@nestjs/common": "^12.0.1",
@@ -32,6 +33,7 @@
     "@nestjs/event-emitter": "^12.0.1",
     "@nestjs/graphql": "^14.0.0",
     "@nestjs/platform-express": "^12.0.1",
+    "@nestjs/schedule": "^12.0.2",
     "@nestjs/typeorm": "^12.0.1",
     "@prisma/adapter-pg": "^7.10.0",
     "@prisma/client": "^7.10.0",
@@ -39,6 +41,7 @@
     "better-auth": "^1.7.2",
     "class-transformer": "^0.5.1",
     "class-validator": "^0.15.1",
+    "file-type": "^22.1.1",
     "graphql": "^16.14.2",
     "nodemailer": "^10.0.0",
     "pg": "^8.23.0",
@@ -53,6 +56,7 @@
     "@nestjs/schematics": "^12.0.0",
     "@nestjs/testing": "^12.0.1",
     "@types/express": "^5.0.0",
+    "@types/multer": "^2.3.0",
     "@types/node": "^24.0.0",
     "@types/pg": "^8.23.1",
     "@types/supertest": "^7.0.0",