P4: persona noun — Agent + ToRunnable bridge + Memory store

The headline P4 piece (clean redesign): the Agent persona noun, decoupled from
its Discord shell.
- agent.go/storage.go/builtin_loader.go moved from mort's pkg/logic/agents; the
  Storage seam drops the Discord CommandBindingStorage embedding (a host
  concern). The host-entangled files (commands, chatbot_provider, command-
  binding dispatcher, personalization, system) stay in mort.
- runnable.go: Agent.ToRunnable() lowers a persona into run.RunnableAgent — the
  bridge that lets run.Executor run a persona without importing this battery
  (the inversion of agentexec.Run(*agents.Agent)).
- memory.go: NewMemory() — zero-dep in-process persona Storage (all 11 CRUD +
  trigger-query methods).

Tests: ToRunnable field/phase mapping; Memory round-trip. CI invariant: core
imports ZERO from persona.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

go.sum

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