Add concurrency control to prevent parallel deploys

- Both workflows share 'pages-deploy' concurrency group
- Build workflow ignores inbox/*.eml and import/*.html paths
- Prevents race conditions between newsletter processing and regular builds

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: pubino

.github/workflows/build.yml

@@ -14,8 +14,14 @@ on:
       - 'CNAME'
       - '.gitignore'
       - '.dockerignore'
+      - 'inbox/*.eml'
+      - 'import/*.html'
   workflow_dispatch:
 
+concurrency:
+  group: pages-deploy
+  cancel-in-progress: false
+
 jobs:
   build:
     runs-on: ubuntu-latest

.github/workflows/process-newsletters.yml

@@ -7,6 +7,10 @@ on:
       - 'import/*.html'
   workflow_dispatch:
 
+concurrency:
+  group: pages-deploy
+  cancel-in-progress: false
+
 jobs:
   process:
     runs-on: ubuntu-latest