Replace the monolithic agents config with a cleaner structure:
- llm: holds provider credentials and default model settings
- probo-agent: LLM overrides for the probo agent
- evidence-describer: worker config (interval, stale-after,
max-concurrency) alongside LLM overrides
This makes worker tuning configurable via YAML and env vars
instead of being hardcoded in Go, and separates provider
credentials from per-consumer model settings.
Signed-off-by: Bryan Frimin <bryan@getprobo.com>