ci: serve docs from develop only

Docs deploy to GitHub Pages from develop for faster iteration cycles.
Main was failing the deploy step with "Branch 'main' is not allowed to
deploy to github-pages due to environment protection rules" on every
release merge (v3.2.0, v3.3.0) — noise without signal, since docs
weren't meant to serve from main anyway.

Removes main from both the push trigger and the deploy-job guard.
Develop continues to deploy as before; manual dispatch still works.

.github/workflows/deploy-docs.yml

@@ -2,7 +2,7 @@ name: Deploy Docs
 
 on:
   push:
-    branches: [main, develop]
+    branches: [develop]
     paths:
       - ".github/workflows/deploy-docs.yml"
       - "website/**"
@@ -51,7 +51,7 @@ jobs:
           path: website/.vitepress/dist
 
   deploy:
-    if: github.ref_name == 'main' || github.ref_name == 'develop'
+    if: github.ref_name == 'develop'
     environment:
       name: github-pages
       url: ${{ steps.deployment.outputs.page_url }}