add local ciphertext storage module to backend.

Bind-mount backend/uploads in dev; path helpers with traversal guards and Jest coverage for StorageService.

backend/package.json

@@ -12,7 +12,12 @@
         "typeorm:run-migrations": "npm run typeorm migration:run -- -d ./src/database/DataSource.ts",
         "typeorm:generate-migration": "npm run typeorm -- -d ./src/database/DataSource.ts migration:generate ./src/database/migrations/$npm_config_name",
         "typeorm:revert-migration": "npm run typeorm -- -d ./src/database/DataSource.ts migration:revert",
-        "typeorm:create-migration": "npm run typeorm -- migration:create ./src/database/migrations/$npm_config_name"
+        "typeorm:create-migration": "npm run typeorm -- migration:create ./src/database/migrations/$npm_config_name",
+        "test": "jest"
+    },
+    "jest": {
+        "preset": "ts-jest",
+        "rootDir": "src"
     },
     "dependencies": {
         "@nestjs/common": "^11.0.1",
@@ -30,8 +35,11 @@
         "@nestjs/cli": "^11.0.24",
         "@nestjs/schematics": "^11.0.0",
         "@types/express": "^5.0.0",
+        "@types/jest": "^30.0.0",
         "@types/node": "^22.10.7",
         "@types/pg": "^8.23.1",
+        "jest": "^30.5.2",
+        "ts-jest": "^29.4.14",
         "ts-node": "^10.9.2",
         "tsconfig-paths": "^4.2.0",
         "typescript": "~6.0.2"