Add workflow concurrency control to prevent concurrent CI runs

Added concurrency groups to both CI and Deploy workflows to:
- Queue jobs per workflow and branch combination
- Cancel older runs when new commits are pushed
- Prevent resource conflicts on self-hosted runners

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

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

.forgejo/workflows/ci.yml

@@ -6,6 +6,10 @@ on:
   pull_request:
     branches: [ main, master ]
 
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: true
+
 jobs:
   test:
     runs-on: self-hosted

.forgejo/workflows/deploy.yml

@@ -5,6 +5,10 @@ on:
     branches: [ main, master ]
   workflow_dispatch:
 
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: true
+
 jobs:
   deploy:
     runs-on: self-hosted