[EPIC] Spring Boot + azd

A developer with a working Spring Boot application should be able to run `azd up` and get it running in Azure without first becoming an Azure expert or describing the application again in `azure.yaml`. The project already tells us how it builds, which services it contains, and many of the dependencies it needs. The extension should use that information to produce a secure, observable, and repeatable deployment, with Azure Container Apps as the default destination and Spring conventions preserved for configuration and local development.

This epic is deliberately limited to the Spring Boot extension and extension-owned assets. General capabilities belong to [Invisible Azure](https://github.com/Azure/azure-dev/issues/9835), [Layered provisioning](https://github.com/Azure/azure-dev/issues/9765), or another core epic. Those capabilities are dependencies here, not work to absorb into this epic. The extension must integrate entirely through standard `azd` commands and supported extension points. It must not introduce any Spring-specific commands or verbs.

The entry point named by the issue is `azd up`; begin by tracing the Spring Boot extension's standard `azd` integration and the information currently represented in `azure.yaml`. Confirm the extension-owned deployment path targets Azure Container Apps, preserves Spring configuration and local-development conventions, and keeps security, observability, and repeatability requirements; done means a working Spring Boot app deploys without repeating its application description or adding Spring-specific commands.

Written by the indexing model from the issue text.