docs: document greet() return format and default parameter

## Docs drift detected

`src/hello.js` returns `"Bonjour, ${name}!"` with a default parameter of `"world"`, but `docs/overview.md` only described the function as "returns a greeting string" without specifying the format or default.

## Changes

- `docs/overview.md`: Added return value format, default parameter, and usage examples.

## Review notes

- No source code was changed — docs only.
- Verify the greeting format matches the current implementation in `src/hello.js`.

> Generated by [Tier 1 / Docs drift (gh-aw)](https://github.com/bcgov/tier1-pattern-test/actions/runs/31999986251) · 21.4 AIC · ⌖ 4.84 AIC · ⊞ 5.1K · [◷](https://github.com/search?q=repo%3Abcgov%2Ftier1-pattern-test+%22gh-aw-workflow-id%3A+tier1-docs-drift%22&type=pullrequests)

---

> [!NOTE]
> This was originally intended as a pull request, but GitHub Actions is not permitted to create or approve pull requests in this repository.
> The changes have been pushed to branch `docs/update-greet-overview-eb0858bc0ce87edd`.
>
> **[Click here to create the pull request](https://github.com/bcgov/tier1-pattern-test/compare/main...docs/update-greet-overview-eb0858bc0ce87edd?expand=1&title=docs%3A%20document%20greet()%20return%20format%20and%20default%20parameter)**

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Show patch (34 lines)

```diff
From 1b4d370834b8b8774fadb257b7bc6e97ab8b922e Mon Sep 17 00:00:00 2001
From: "github-actions[bot]"
Date: Mon, 17 Aug 2026 06:03:15 +0000
Subject: [PATCH] docs: document greet() return format and default parameter

- Add return value format: "Bonjour, !"
- Document default parameter value ("world")
- Add usage examples

Detected by Tier 1 docs-drift check.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
---
docs/overview.md | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/docs/overview.md b/docs/overview.md
index baa0f7d..10bb084 100644
--- a/docs/overview.md
+++ b/docs/overview.md
@@ -1,5 +1,8 @@
# Overview

-`greet(name)` returns a greeting string.
+`greet(name)` returns a greeting string in the format `"Bonjour, !"`.
+
+- **Parameter**: `name` (string, default: `"world"`)
+- **Returns**: A string such as `"Bonjour, world!"` or `"Bonjour, Alice!"`

(Intentionally simple — change `src/hello.js` without updating this file to exercise docs drift.)
--
2.54.0

```

Compare the implementation in src/hello.js with the documentation in docs/overview.md. The proposed documentation changes are already on branch docs/update-greet-overview-eb0858bc0ce87edd; done means docs/overview.md accurately states the greeting format, default parameter, and examples.

Written by the indexing model from the issue text.