docs: add bearer auth server example

[LiJzd]

Summary

• Replace the placeholder authorization docs page with a focused bearer-token server example.
• Show how to configure TokenVerifier and AuthSettings for protected MCP tools.
• Clarify that the same bearer-token middleware applies to SSE and Streamable HTTP, including the default Inspector URLs and auth failure behavior.

Duplicate-work check

• Checked open PRs for 431 OR Bearer header SSE auth.
• Checked open PRs for Bearer auth SSE example.
• No open documentation PR appeared to address the basic bearer-token SSE/Streamable HTTP example requested in Question: How to authorise a client with Bearer header with SSE? #431.

Validation

• git diff --check
• Parsed the Python code block in docs/authorization.md with ast.parse.
• Checked that only docs/authorization.md changed.

Note: I could not run the repository's recommended uv run --frozen ... checks because uv is not installed on this machine.

Addresses #431.

AI assistance disclosure

This documentation update was prepared with AI assistance and manually reviewed before submission.