fix(templates): versions in agent templates should be pinned to avoid breakages.

### Problem
Many versions in agent templates are left unpinned. This allows for new major releases (or any breaking change) to break projects completely.

More info in: https://github.com/aws/agentcore-cli/pull/1850.

Example of a dependency that is still pinned: https://github.com/aws/agentcore-cli/blob/main/src/assets/python/agui/langchain_langgraph/base/pyproject.toml#L24

If langgraph releases a new major version that isn't compatible with our code, all projects will break.

The same is true for the TS projects. We already pin CDK versions, but we need to pin all versions.

### Definition of Done
- Investigate pinning or "partially pinning" via https://peps.python.org/pep-0440/#compatible-release (and the TS equiv) to ensure new releases don't break projects. We can't blindly pin everything since newer versions may already be resolved such that pinning changes behavior.
- Ensure that projects cannot be broken by external releases.

Start by reading linked pull request 1850 and the pinned dependency example in src/assets/python/agui/langchain_langgraph/base/pyproject.toml. Inspect the Python and TypeScript agent templates for unpinned dependencies, then compare Python compatible-release guidance with its TypeScript equivalent. Done means external releases cannot introduce breaking changes across the templates.

Written by the indexing model from the issue text.