Hardcoded Google Analytics Tracking ID

**Task description**:
- The docusaurus.config.js file currently includes a hardcoded Google Analytics tracking ID.
- Although it’s not sensitive, it’s better practice to load it from an environment variable instead of committing it to source control.

**Current:**
`trackingID: "G-XXXXXXX",`

**Proposed:**
`trackingID: process.env.GA_TRACKING_ID,`

**Solution**:

- Remove hardcoded ID
- Add GA_TRACKING_ID to GitHub Secrets
- Update build workflow to use the secret

**GitHub Actions example:**
```
- name: Build Docusaurus
run: npm run build
env:
GA_TRACKING_ID: ${{ secrets.GA_TRACKING_ID }}
```

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