feat: add different agents with easy configs

[maximilien]

• search agent
• rag agent
• query agent
• eval agent

[maximilien]

✅ Progress Update: The weave config agents command has been implemented in v0.8.3, providing infrastructure for agent configuration via weave-agents.yaml. However, the specific agent types (search, rag, query, eval) mentioned in this issue still need implementation. Partial completion - keeping open for remaining agent types.

[maximilien]

Stale check: no activity in 7+ days. If this is still desired, propose a scoped MVP and we’ll prioritize accordingly.