Small doc changes.

[tjsullivan1]

This pull request includes updates to dependencies, environment configuration, and documentation to improve setup clarity and validation for the MCP and backend services. The most important changes are grouped below:

Dependency Updates:

• Updated the semantic-kernel dependency in pyproject.toml to require version >=1.35 for improved compatibility and stability.
• I was going to pin versions for everything, but the uv.lock files should also do that for us.

Environment and Configuration:

• Updated the local MCP server URI example in .env.sample to use /mcp instead of /sse, aligning the sample with actual endpoint usage.

Documentation Improvements:

• Added a sample curl command in docs/01_mcp_uv.md to help users verify that the MCP server is online and accepting requests.
• Added a sample curl command in docs/02_backend_uv.md for validating that the backend service is running and can accept chat requests.