Explicit, per-agent selection of the pluggable behaviours.

One {module, opts} ref per behaviour plus the two first-class hook lists. hooks is an ordered list of Normandy.Behaviours.Hooks entries, persisted with the refs. Carried on BaseAgentConfig.behaviours; defaults to the all-defaults bundle, so the "everything off" path is observably identical to today.

to_pipeline/1 adapts the dispatch-path slots (policy, budget, before_hooks, after_hooks, and the before_tool/after_tool callbacks of hooks) into a %Normandy.Agents.Dispatch.Pipeline{}. Classification (policy, before_hooks) gets the agent's whole config; execution (budget, the tool, after_tool, after_hooks) runs in a tool task whose config has the memory without its entries (the turn id stays), on every shell. Building it here (not on Dispatch) keeps the Phase 1 chokepoint untouched — the dependency points Phase 2 → Phase 1. The credential, compactor and model_catalog slots are not dispatch-path concerns and are not placed on the pipeline. credential has no default: a Normandy.Behaviours.CredentialProvider ref is needed only by a Turn.Session with a :template_provider, which refuses a config without one. compactor selects the :steering-boundary compaction strategy. Where sessions persist is not chosen here: Normandy.Agents.Turn.Server takes :store and :registry (the 1.x session_store/session_registry slots were never read and are gone).