[spindle/test] fix lint errors for backend, use pnpm for workflows

.tangled/workflows/build_backend.yaml

···
 dependencies:
   nixpkgs:
     - nodejs
+    - pnpm
 
 steps:
   - name: "Install dependencies"
-    command: "npm install -C ./backend/"
+    command: "pnpm install -C ./backend/"
     environment:
       NODE_ENV: "development"
       CI: true
 
   - name: "Run linter"
-    command: "npm run lint -C ./backend/"
+    command: "pnpm run lint -C ./backend/"
 
   - name: "Build application"
-    command: "npm run build -C ./backend/"
+    command: "pnpm run build -C ./backend/"
     environment:
       NODE_ENV: "production"
 

.tangled/workflows/build_frontend.yaml

···
 dependencies:
   nixpkgs:
     - nodejs
+    - pnpm
 
 steps:
   - name: "Install dependencies"
-    command: "npm install -C ./frontend/"
+    command: "pnpm install -C ./frontend/"
     environment:
       NODE_ENV: "development"
       CI: true
 
   - name: "Build frontend"
-    command: "npm run build -C ./frontend/"
+    command: "pnpm run build -C ./frontend/"
 
 clone:
   skip: false

.tangled/workflows/build_lexicons.yaml

···
 dependencies:
   nixpkgs:
     - nodejs
+    - pnpm
 
 steps:
   - name: "Install dependencies"
-    command: "npm install -C ./lexicons/"
+    command: "pnpm install -C ./lexicons/"
     environment:
       NODE_ENV: "development"
       CI: true
 
   - name: "Generate lexicons"
-    command: "npm run generate -C ./lexicons/"
+    command: "pnpm run generate -C ./lexicons/"
 
   - name: "Build package"
-    command: "npm run prepublish -C ./lexicons/"
+    command: "pnpm run prepublish -C ./lexicons/"
     environment:
       NODE_ENV: "production"
 

backend/package.json

···
 	"type": "module",
 	"main": "src/main.ts",
 	"engines": {
-		"node": ">=24"
+		"node": ">=22.16.0"
 	},
 	"dependencies": {
 		"@atcute/atproto": "^3.1.0",