ci: add GitLab CI/CD pipeline configuration for Vercel and update gitignore for build artifacts

.gitignore

@@ -34,9 +34,13 @@ yarn-error.log*
 .env*
 !.env.example
 
-# vercel
+# vercel & build cache
 .vercel
+.pnpm-store
 
 # typescript
 *.tsbuildinfo
 next-env.d.ts
+
+.vercel
+.env*

.gitlab-ci.yml

+# GitLab CI/CD Pipeline for deploying Next.js to Vercel using Vercel CLI
+# Reference: https://vercel.com/kb/guide/how-can-i-use-gitlab-pipelines-with-vercel
+
+image: node:20-alpine
+
+stages:
+  - deploy
+
+variables:
+  PNPM_HOME: "/root/.local/share/pnpm"
+  PATH: "$PNPM_HOME:$PATH"
+
+before_script:
+  - npm install -g pnpm vercel
+  - pnpm config set store-dir .pnpm-store
+
+# Cache pnpm dependencies and Next.js build cache to speed up pipelines
+cache:
+  key:
+    files:
+      - pnpm-lock.yaml
+  paths:
+    - .pnpm-store
+    - .next/cache
+
+# 1. Preview Deployment (Triggered on feature branches and Merge Requests)
+deploy_preview:
+  stage: deploy
+  rules:
+    - if: '$CI_COMMIT_BRANCH != "main" && $CI_COMMIT_BRANCH != "master"'
+  script:
+    - vercel pull --yes --environment=preview --token=$VERCEL_TOKEN
+    - vercel build --token=$VERCEL_TOKEN
+    - vercel deploy --prebuilt --token=$VERCEL_TOKEN
+  variables:
+    VERCEL_ORG_ID: $VERCEL_ORG_ID
+    VERCEL_PROJECT_ID: $VERCEL_PROJECT_ID
+
+# 2. Production Deployment (Triggered only when merging into main/master)
+deploy_production:
+  stage: deploy
+  rules:
+    - if: '$CI_COMMIT_BRANCH == "main" || $CI_COMMIT_BRANCH == "master"'
+  script:
+    - vercel pull --yes --environment=production --token=$VERCEL_TOKEN
+    - vercel build --prod --token=$VERCEL_TOKEN
+    - vercel deploy --prebuilt --prod --token=$VERCEL_TOKEN
+  variables:
+    VERCEL_ORG_ID: $VERCEL_ORG_ID
+    VERCEL_PROJECT_ID: $VERCEL_PROJECT_ID