feat: Complete stub services with real implementations and graceful not-configured responses

- ChangelogService: inject PlatformChangelog repo, query with findAndCount(skip/take), return actual data
- ChangelogModule: add TypeOrmModule.forFeature([PlatformChangelog])
- MapsService: add uploadMap() — SHA-256 checksum, storage path, full entity save
- MapsController: add POST /maps/upload with FileInterceptor, map.manage permission, @UploadedFile
- AuthService: replace console.log stubs with Logger; forgotPassword returns 200 with clear message; resetPassword throws NotImplementedException
- PluginsService: searchUmod returns { results: [], message: 'not yet configured' } instead of bare []
- SteamService: add Logger.warn on every stub path (checkForceWipe, getPlayerSummary)
- SettingsService: add Logger; both Cloudflare DNS stubs emit Logger.warn before DB save
- MigrationService: add Logger; exportConfig logs warning + returns note field; importConfig throws NotImplementedException
- Install @types/multer dev dependency for Express.Multer.File type support

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend-nest/package-lock.json

@@ -39,6 +39,7 @@
         "@nestjs/cli": "^10.4.0",
         "@nestjs/schematics": "^10.1.0",
         "@types/express": "^4.17.21",
+        "@types/multer": "^2.0.0",
         "@types/node": "^20.12.0",
         "@types/passport-jwt": "^4.0.1",
         "@types/qrcode": "^1.5.5",
@@ -1256,6 +1257,16 @@
       "dev": true,
       "license": "MIT"
     },
+    "node_modules/@types/multer": {
+      "version": "2.0.0",
+      "resolved": "https://registry.npmjs.org/@types/multer/-/multer-2.0.0.tgz",
+      "integrity": "sha512-C3Z9v9Evij2yST3RSBktxP9STm6OdMc5uR1xF1SGr98uv8dUlAL2hqwrZ3GVB3uyMyiegnscEK6PGtYvNrjTjw==",
+      "dev": true,
+      "license": "MIT",
+      "dependencies": {
+        "@types/express": "*"
+      }
+    },
     "node_modules/@types/node": {
       "version": "20.19.33",
       "resolved": "https://registry.npmjs.org/@types/node/-/node-20.19.33.tgz",