feat(workflows): add Codex automation for issue processing

- Introduced a new GitHub Actions workflow `codex.yml` to automate
  issue processing using OpenAI Codex.
- Configured the workflow to trigger on issue creation with titles
  containing `[codex]`.
- Added steps to:
  - Install Codex CLI and process issues with custom instructions.
  - Create a new branch and commit changes if modifications are made.
  - Automatically open a pull request and comment on the issue.
- Utilized GitHub Models API for Codex inference with GPT-4.1.

Author: hazadus

.github/workflows/codex.yml

@@ -0,0 +1,65 @@
+# Source: https://gist.github.com/sgoedecke/2b4e8d5e6b21f536ea399f1728916ad5
+name: Codex on GitHub Models
+
+on:
+  issues:
+    types: [opened]
+
+jobs:
+  process-issue:
+    if: contains(github.event.issue.title, '[codex]')
+    runs-on: ubuntu-latest
+    permissions:
+      contents: write
+      issues: write
+      pull-requests: write
+      models: read
+
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v3
+
+      - name: Setup Node.js
+        uses: actions/setup-node@v3
+        with:
+          node-version: '22'
+
+      - name: Install Codex CLI
+        run: npm install -g @openai/codex
+
+      - name: Process issue with Codex
+        env:
+          OPENAI_API_KEY: ${{ secrets.GITHUB_TOKEN }}
+          ISSUE_BODY: ${{ github.event.issue.body }}
+          ISSUE_NUMBER: ${{ github.event.issue.number }}
+          ISSUE_TITLE: ${{ github.event.issue.title }}
+          GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+        run: |
+          INSTRUCTION="$ISSUE_TITLE  --- $ISSUE_BODY"
+          
+          BRANCH_NAME="codex/issue-$ISSUE_NUMBER"
+          git checkout -b $BRANCH_NAME
+
+          export OPENAI_BASE_URL=https://models.github.ai/inference
+
+          # any provider string would work here, it's just so codex knows it's using a custom model
+          codex --approval-mode full-auto --provider github --model openai/gpt-4.1 "$INSTRUCTION"
+          
+          if [[ -n $(git status --porcelain) ]]; then
+            git config user.name "GitHub Models Codex Bot"
+            git config user.email "github-models-codex-bot@noreply.github.com"
+            
+            git add .
+            git commit -m "Codex changes for issue #$ISSUE_NUMBER"
+            git push origin $BRANCH_NAME
+            
+            # Create PR and comment on issue using the same token
+            gh pr create --title "Codex: ${{ github.event.issue.title }}" \
+              --body "Auto-generated by Codex for issue #$ISSUE_NUMBER" \
+              --base ${{ github.event.repository.default_branch }} \
+              --head $BRANCH_NAME
+              
+            gh issue comment $ISSUE_NUMBER --body "Codex created a PR for this issue"
+          else
+            gh issue comment $ISSUE_NUMBER --body "Codex processed this issue but made no changes"
+          fi