Fix and document the Tinybird benchmark runner

[fallintoplace]

Summary

• replace the invalid placeholder authorization header with required TINYBIRD_TOKEN and TINYBIRD_HOST environment variables
• fail on shell, HTTP, malformed JSON, and non-numeric timing errors
• document the Tinybird CLI setup, data import, pipe generation, token creation, and benchmark invocation
• use the host selected by tb auth -i, preserve runner failures when logging with tee, and ignore local credentials and virtual environments

Why

AUTH_HEADER=<TOKEN> is parsed as shell redirection, so the runner exits before sending any benchmark requests. The previous instructions also did not cover the setup needed to create the 43 pipe endpoints and run the benchmark.

Validation

• bash -n tinybird/run.sh
• verified missing token and host values fail before any request
• mocked successful Tinybird responses and verified the output contains 43 arrays with three numeric timings each
• verified malformed and non-numeric timing responses fail
• git diff --check

[rschu1ze]

I created a Tinybird account but the UI is rather complex and this README covers it only rudimentary.

@fallintoplace Since you seem familiar with Tinybird, maybe I could ask you to add

• the steps to install the Tinybird CLI in section "Creating an account" above,
• the steps to create and retrieve a "Tinybird Token" (l. 35),
• the steps to run the INSERT (l. 24),
• the exact invocation of run.sh (the PR message has an example)