Remove `todo-python-mongo-terraform` from Learn docs

# Replace `todo-python-mongo-terraform` template  in Microsoft Learn examples

## Background
Microsoft Learn currently references `Azure-Samples/todo-python-mongo-terraform` template in:

- [Dedicated sample page](https://learn.microsoft.com/en-us/samples/azure-samples/todo-python-mongo-terraform/todo-python-mongo-terraform/)
- [Azure Developer CLI full-stack templates](https://learn.microsoft.com/en-us/azure/developer/azure-developer-cli/full-stack-templates?tabs=react%2Caspnet)

Replace this sample with `hello-azd` (or a python template).

## Tasks

- [ ] Remove or redirect the dedicated sample page, following Microsoft Learn guidance.
- [ ] Replace its full-stack templates entry with   .
- [ ] Update associated descriptions, repository links, and commands.
- [ ] Search the documentation source for any remaining references to: `todo-python-mongo-terraform` and `Azure-Samples/todo-python-mongo-terraform`
- [ ] Validate all affected links.

## Acceptance criteria

- [ ] The old sample page is removed or redirected appropriately.
- [ ] The full-stack templates page lists the replacement sample.
- [ ] No documentation or commands reference the old repository.
- [ ] Replacement links and commands use the confirmed repository.
- [ ] Documentation and link-validation checks pass.
- [ ] All    placeholders are resolved before publication.