docs: align client config examples with active servers

[go165]

Summary

• Replace archived GitHub/Postgres entries in the root README client config example with active Fetch/Time reference servers
• Keep the Windows note accurate by naming the uvx examples that do not need the npx wrapper

Validation

• git diff --check
• Checked the example command names against src/fetch/README.md, src/time/README.md, and src/time/pyproject.toml

No code changes.

[go165]

/i-promise-this-is-not-a-new-server

This PR updates the root README client configuration examples to use existing active reference servers already maintained in this repository. It does not add a new server listing.