Add automatic VERSION setting for nightly builds

- Modified build.yml to accept optional version input parameter
- Modified nightly.yml to calculate VERSION from build date in format yymmddb
- VERSION is passed as PLATFORMIO_BUILD_FLAGS to override default in wled.h
- Other workflows (wled-ci.yml, release.yml) unchanged and will use default VERSION

Co-authored-by: softhack007 <91616163+softhack007@users.noreply.github.com>

.github/workflows/nightly.yml

@@ -8,8 +8,25 @@ on:
   workflow_dispatch:
 
 jobs:
+  calculate_version:
+    name: Calculate VERSION
+    runs-on: ubuntu-latest
+    outputs:
+      version: ${{ steps.version.outputs.version }}
+    steps:
+      - name: Calculate VERSION
+        id: version
+        run: |
+          # VERSION format: yymmddb (b = daily build number, set to 1 for nightly)
+          VERSION=$(date -u +"%y%m%d")1
+          echo "version=$VERSION" >> $GITHUB_OUTPUT
+          echo "Calculated VERSION: $VERSION"
+  
   wled_build:
+    needs: calculate_version
     uses: ./.github/workflows/build.yml
+    with:
+      version: ${{ needs.calculate_version.outputs.version }}
   nightly:
     name: Deploy nightly
     runs-on: ubuntu-latest