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

[MadhuraBharadwaj-MSFT]

This sample and 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