Merge with `m365-inbox-agent-functions-markdown` into a single sample

This sample and [`m365-inbox-agent-functions-markdown`](https://github.com/Azure-Samples/m365-inbox-agent-functions-markdown) should be merged into a single repo to avoid the maintenance overhead of two near-duplicate samples and to give users one canonical place to start.

## Proposed plan
1. Decide which repo survives (or create a new umbrella).
2. Move/consolidate code into the surviving repo.
3. Archive the other with a pointer banner.

Tracking issue (Markdown side): [_issue_](https://github.com/Azure-Samples/m365-inbox-agent-functions-markdown/issues/3)

Start by comparing this repository with m365-inbox-agent-functions-markdown and read the linked tracking issue (#3). Decide which repository survives or whether an umbrella is needed, then define the consolidation and archive pointer. Done means one canonical sample repository and a pointer from the archived repository.

Written by the indexing model from the issue text.