Implement the agent on a single service

[alexduf]

The somewhat vibe-coded agent prototype here seems to be working.

There isn't much clean-up to do, but:

• it was written by an LLM, we need to ensure we understand every single line
• we want to start writing the log lines into separate files named twirl-templates.jsonl
• we'll flush writing to disk after each write.

Writing / flushing on each log line may seem expensive, but I don't think we need to go as far as writing to file from a separate thread as it should only do IO the very first time a template is encountered. The trade-off is performance vs simplicity, and I think simplicity of the agent wins here.