Use synth_only build mode for faster CI

.github/workflows/main.yaml

@@ -24,6 +24,8 @@ on:
 env:
   lock_pdm: ${{ ! (github.ref_name == 'refs/heads/latest-release' || inputs.release) }}
   BACKEND_VERSION: ${{ inputs.backend_version || github.event.client_payload.backend_version || vars.CHIPFLOW_BACKEND_VERSION }}
+  # Use synth_only for all CI (faster), full only for backend-test (tests complete pipeline)
+  BUILD_MODE: ${{ github.event_name == 'repository_dispatch' && 'full' || 'synth_only' }}
 
 name: CI
 run-name: ${{ github.event_name == 'repository_dispatch' && format('Backend Test - {0}', github.event.client_payload.backend_version) || (inputs.backend_version && format('CI - Backend {0}', inputs.backend_version) || (inputs.release && 'Release' || 'CI')) }}
@@ -35,6 +37,18 @@ jobs:
       matrix:
         design: ['mcu_soc', 'minimal']
     steps:
+      - name: Parse PR body for backend version override
+        id: pr-config
+        if: github.event_name == 'pull_request'
+        env:
+          PR_BODY: ${{ github.event.pull_request.body }}
+        run: |
+          # Extract BACKEND_VERSION from PR body (format: BACKEND_VERSION: <value>)
+          if [[ "$PR_BODY" =~ BACKEND_VERSION:[[:space:]]*([^[:space:]]+) ]]; then
+            echo "backend_version=${BASH_REMATCH[1]}" >> $GITHUB_OUTPUT
+            echo "Found BACKEND_VERSION override: ${BASH_REMATCH[1]}"
+          fi
+
       - name: Check out source code
         uses: actions/checkout@v4
 
@@ -69,7 +83,9 @@ jobs:
         env:
           CHIPFLOW_API_KEY: ${{ secrets.CHIPFLOW_API_KEY}}
           CHIPFLOW_API_ORIGIN: ${{ vars.CHIPFLOW_API_ORIGIN }}
-          CHIPFLOW_BACKEND_VERSION: ${{ env.BACKEND_VERSION }}
+          # Priority: PR body override > workflow input > repository_dispatch > vars
+          CHIPFLOW_BACKEND_VERSION: ${{ steps.pr-config.outputs.backend_version || env.BACKEND_VERSION }}
+          CHIPFLOW_BUILD_MODE: ${{ env.BUILD_MODE }}
 
   test:
     runs-on: ubuntu-latest