Fix GitHub Actions PR creation permission errors by standardizing token usage and adding documentation.

## Summary

Fixed PR creation failures in GitHub Actions workflows by standardizing token usage to `github.token` and adding clear documentation headers explaining the required repository permission setting.

## Files Changed

### Modified (2 files)

- `.github/workflows/dispatch-erk-queue.yml` - Added documentation header with required repository setting
- `.github/workflows/implement-plan.yml` - Added documentation header and standardized token reference

## Key Changes

- Standardized token usage in `implement-plan.yml` checkout action from `${{ secrets.GITHUB_TOKEN }}` to `${{ github.token }}`
- Added identical documentation headers to both workflow files explaining the required "Allow GitHub Actions to create and approve pull requests" repository setting
- Provided clear error message context in documentation for troubleshooting PR creation failures

## Critical Notes

- GitHub token permission setting must be enabled in repository settings under Actions > General > Workflow permissions for workflows to successfully create pull requests

Author: schrockn

.github/workflows/dispatch-erk-queue.yml

@@ -1,3 +1,10 @@
+# REQUIRED REPOSITORY SETTING:
+# Settings > Actions > General > Workflow permissions
+# ✓ Enable "Allow GitHub Actions to create and approve pull requests"
+#
+# Without this setting, PR creation will fail with:
+# "GitHub Actions is not permitted to create or approve pull requests"
+
 name: Dispatch Erk Queue
 
 on:

.github/workflows/implement-plan.yml

@@ -1,3 +1,10 @@
+# REQUIRED REPOSITORY SETTING:
+# Settings > Actions > General > Workflow permissions
+# ✓ Enable "Allow GitHub Actions to create and approve pull requests"
+#
+# Without this setting, PR creation will fail with:
+# "GitHub Actions is not permitted to create or approve pull requests"
+
 name: Implement Plan
 
 on:
@@ -22,7 +29,7 @@ jobs:
       - uses: actions/checkout@v4
         with:
           ref: ${{ inputs.branch-name || github.ref }}
-          token: ${{ secrets.GITHUB_TOKEN }}
+          token: ${{ github.token }}
 
       - name: Check for submission
         id: check_submission