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.json

@@ -44,6 +44,7 @@
     "@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",