Fix missing mcp__github__create_pull_request in Claude Implementation workflow

## Problem
Claude cannot automatically create pull requests when requested via @claude mentions in GitHub issues, despite being explicitly asked to use `mcp__github__create_pull_request`.

## Root Cause
The `claude-implementation.yml` workflow only includes generic `mcp__github` permission in its `allowed_tools` configuration, but doesn't explicitly list the specific GitHub MCP tools like `mcp__github__create_pull_request`.

## Impact
- Claude reports: "⚠️ PR Creation Note: The mcp__github__create_pull_request tool mentioned in your request is not available"
- Automated PR creation fails in OSE automation workflows
- Manual intervention required to create PRs after Claude completes work

## Investigation Details
Found in issue #1157 where Claude was asked to:
```
CREATE the PR automatically using mcp__github__create_pull_request (not gh cli)
```

But Claude responded:
```
The mcp__github__create_pull_request tool mentioned in your request is not available in my current tool set.
```

## Solution
Update `.github/workflows/claude-implementation.yml` line 76 to explicitly include the GitHub MCP tools:
- `mcp__github__create_pull_request` - for creating PRs
- `mcp__github__get_issue` - for reading issue details
- `mcp__github__add_issue_comment` - for commenting on issues
- `mcp__github__update_issue` - for updating issue status
- `mcp__github__search_issues` - for searching related issues
- `mcp__github__list_pull_requests` - for checking existing PRs
- `mcp__github__merge_pull_request` - for merging PRs (if needed)

## Testing
After fix is deployed, test by creating a new issue and asking Claude to implement it with automatic PR creation.

## Principles
- `systems-stewardship`: Maintaining GitHub Actions workflows for reliable automation
- `ose`: Enabling elevated automation without manual intervention

Inspect .github/workflows/claude-implementation.yml around line 76 and review the allowed_tools configuration. After the workflow change is deployed, create a new issue and ask Claude to implement it with automatic pull-request creation; done means the requested GitHub MCP tools are available and a pull request is created without manual intervention.

Written by the indexing model from the issue text.