feat: optimize frontend CI with shared setup job (#10286)

# Change details
- **Before**: Each job separately installs dependencies (~4 redundant
installations)
  ### Massive Redundancy in Setup Steps
  Each job repeats these SAME 4 steps:
  - Checkout repository
  - Set up Node.js (version 21) 
  - Enable corepack
  - Install dependencies (pnpm install --frozen-lockfile)
  
  This happens 4+ times across different jobs:

   -  lint job
    - type-check job
    - chromatic job
    - test job (runs 2x due to matrix strategy)
    
   ### No Dependency Caching
  No caching strategy - downloads packages fresh every time
   - Every workflow run downloads all packages from scratch
   - No benefit from previous runs, even with identical pnpm-lock.yaml


- **After**: Dependencies installed once in setup job, cached and reused

This optimization maintains all existing CI functionality while
significantly improving pipeline efficiency.
A workflow run example is dispatched:
https://github.com/souhailaS/AutoGPT/actions/workflows/platform-frontend-ci.yml


## Additional Context 
We are a team of researchers from University of Zurich
(https://www.ifi.uzh.ch/en/zest.html) currently **working on automating
energy optimizations in GitHub Actions workflows**. This optimization
maintains full functionality while significantly reducing computational
overhead and energy consumption.

souhaila.serbout@uzh.ch

.github/workflows/platform-frontend-ci.yml

@@ -18,11 +18,14 @@ defaults:
     working-directory: autogpt_platform/frontend
 
 jobs:
-  lint:
+  setup:
     runs-on: ubuntu-latest
-
+    outputs:
+      cache-key: ${{ steps.cache-key.outputs.key }}
+    
     steps:
-      - uses: actions/checkout@v4
+      - name: Checkout repository
+        uses: actions/checkout@v4
 
       - name: Set up Node.js
         uses: actions/setup-node@v4
@@ -32,6 +35,45 @@ jobs:
       - name: Enable corepack
         run: corepack enable
 
+      - name: Generate cache key
+        id: cache-key
+        run: echo "key=${{ runner.os }}-pnpm-${{ hashFiles('**/pnpm-lock.yaml') }}" >> $GITHUB_OUTPUT
+
+      - name: Cache dependencies
+        uses: actions/cache@v4
+        with:
+          path: ~/.pnpm-store
+          key: ${{ steps.cache-key.outputs.key }}
+          restore-keys: |
+            ${{ runner.os }}-pnpm-
+
+      - name: Install dependencies
+        run: pnpm install --frozen-lockfile
+
+  lint:
+    runs-on: ubuntu-latest
+    needs: setup
+
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v4
+
+      - name: Set up Node.js
+        uses: actions/setup-node@v4
+        with:
+          node-version: "21"
+
+      - name: Enable corepack
+        run: corepack enable
+
+      - name: Restore dependencies cache
+        uses: actions/cache@v4
+        with:
+          path: ~/.pnpm-store
+          key: ${{ needs.setup.outputs.cache-key }}
+          restore-keys: |
+            ${{ runner.os }}-pnpm-
+
       - name: Install dependencies
         run: pnpm install --frozen-lockfile
 
@@ -40,9 +82,11 @@ jobs:
 
   type-check:
     runs-on: ubuntu-latest
+    needs: setup
 
     steps:
-      - uses: actions/checkout@v4
+      - name: Checkout repository
+        uses: actions/checkout@v4
 
       - name: Set up Node.js
         uses: actions/setup-node@v4
@@ -52,6 +96,14 @@ jobs:
       - name: Enable corepack
         run: corepack enable
 
+      - name: Restore dependencies cache
+        uses: actions/cache@v4
+        with:
+          path: ~/.pnpm-store
+          key: ${{ needs.setup.outputs.cache-key }}
+          restore-keys: |
+            ${{ runner.os }}-pnpm-
+
       - name: Install dependencies
         run: pnpm install --frozen-lockfile
 
@@ -60,10 +112,13 @@ jobs:
 
   chromatic:
     runs-on: ubuntu-latest
+    needs: setup
     # Only run on dev branch pushes or PRs targeting dev
     if: github.ref == 'refs/heads/dev' || github.base_ref == 'dev'
+    
     steps:
-      - uses: actions/checkout@v4
+      - name: Checkout repository
+        uses: actions/checkout@v4
         with:
           fetch-depth: 0
 
@@ -75,6 +130,14 @@ jobs:
       - name: Enable corepack
         run: corepack enable
 
+      - name: Restore dependencies cache
+        uses: actions/cache@v4
+        with:
+          path: ~/.pnpm-store
+          key: ${{ needs.setup.outputs.cache-key }}
+          restore-keys: |
+            ${{ runner.os }}-pnpm-
+
       - name: Install dependencies
         run: pnpm install --frozen-lockfile
 
@@ -88,6 +151,7 @@ jobs:
 
   test:
     runs-on: ubuntu-latest
+    needs: setup
     strategy:
       fail-fast: false
       matrix:
@@ -125,6 +189,14 @@ jobs:
         run: |
           docker compose -f ../docker-compose.yml up -d
 
+      - name: Restore dependencies cache
+        uses: actions/cache@v4
+        with:
+          path: ~/.pnpm-store
+          key: ${{ needs.setup.outputs.cache-key }}
+          restore-keys: |
+            ${{ runner.os }}-pnpm-
+
       - name: Install dependencies
         run: pnpm install --frozen-lockfile