Upgrade Hugo to 0.146.0 and install Docsy NPM dependencies

The Docsy v0.12.0 theme requires Hugo 0.146.0+ and uses Bootstrap/FontAwesome
as NPM dependencies rather than Hugo modules.

Changes:
- Upgraded Hugo from 0.135.0 to 0.146.0 (minimum required by Docsy v0.12.0)
- Added npm install step in Docsy theme directory to install Bootstrap 5.3.6
  and FontAwesome 6.7.2 from theme's package.json

The theme's hugo.yaml mounts these from node_modules/ directories. No Go
installation or Hugo module commands needed.

Tested with act - build completes successfully.

Author: kaxil

.github/workflows/build.yml

@@ -80,12 +80,11 @@ jobs:
       - name: 📚 Install Hugo
         uses: peaceiris/[email protected]  # v3.0.0
         with:
-          hugo-version: '0.135.0'
+          hugo-version: '0.146.0'
           extended: true
-      - name: 🔵 Setup Go
-        uses: actions/setup-go@v6
-        with:
-          go-version: '1.23'
+      - name: 📦 Install Docsy theme dependencies (Bootstrap & FontAwesome)
+        working-directory: /mnt/airflow-site/landing-pages/site/themes/docsy
+        run: npm install
       - name: 🟢 Install node dependencies
         run: |
           /mnt/airflow-site/site.sh install-node-deps