LLM outputs backslashes instead of backticks in create_pull_request body, causing path prompts and control character corruption

## Description

When creating pull requests via the `create_pull_request` MCP tool, the PR body sometimes contains backslash-delimited code spans (`\code\`) instead of backtick-delimited spans (`` `code` ``). This causes two problems:

1. **False path detection**: The Copilot CLI interprets `\RequestReviewAsync\` etc. as Windows file paths and prompts the user to "allow paths" for strings that are not paths
2. **Control character corruption**: Backslash sequences that happen to match C-style escapes get interpreted as control characters:
- `\a` (e.g. `\auto_execute`) → U+0007 (bell)
- `\r` (e.g. `\request_review`) → carriage return → newline
- `\t` (e.g. `\task_complete`) → tab (U+0009)
- `\v` (e.g. `\volatile`) → vertical tab (U+000B)
- `\n` → newline (U+000A)
- `\b` → backspace (U+0008)

## Reproduction

This is intermittent — some PRs are clean while others are affected. Examples from https://github.com/m-nash/pr-copilot:

- **PR #34** (affected): Body has `\RequestReviewAsync\` instead of backtick-delimited, `\auto_execute` where `\a` became bell character (U+0007)
- **PR #33** (clean): Same repo, same user, backticks preserved correctly
- **PR #32** (affected): `\[Heartbeat]\`, `\Task.Run\`, `\volatile bool IsLoading\` where `\v` became vertical tab (U+000B)
- **PR #30** (affected): `\ask_user\` where `\a` became bell (U+0007)

## Analysis

1. The GitHub MCP server’s `CreatePullRequest` handler is a clean pass-through — it takes the `body` parameter and sends it directly to `github.NewPullRequest.Body` with no transformation
2. The corruption originates upstream, likely either:
- The LLM itself generates `\code\` instead of `` `code` `` in the JSON tool call arguments (intermittently)
- Or something in the CLI’s JSON parsing/argument extraction converts backticks to backslashes
3. The C-style escape interpretation (`\a`→bell, `\v`→vtab) suggests a non-standard string processing step, since these are NOT valid JSON escape sequences (`\a` and `\v` are C escapes, not JSON)

## Evidence that the LLM generates backslashes

When the issue occurs, the user is prompted to "allow paths" for the backslash-delimited strings in the body argument. This confirms the `\` characters are present in the tool call arguments before they reach the MCP server.

## Expected behavior

- PR bodies should preserve backtick-delimited code spans as-is
- Strings like `\RequestReviewAsync\` in tool arguments should not trigger path access prompts
- No C-style escape interpretation should be applied to PR body text

## Environment

- Copilot CLI on Windows
- GitHub MCP server (latest)
- Affects `create_pull_request` tool body parameter

Start by tracing the create_pull_request MCP tool into the GitHub MCP server’s CreatePullRequest handler, then inspect the CLI’s JSON parsing and argument-extraction path. Compare the body before and after each boundary using the affected examples. Done means backtick code spans remain intact, backslash sequences are not interpreted as control characters, and path prompts are not triggered.

Escrita pelo modelo de indexação a partir do texto da issue.