Add conversation engine tool profiles

[roackb2]

What changed

• add an engine-level toolProfile option to createConversationEngine
• propagate the profile through normalized engine and turn configuration
• use the host profile by default while preserving custom-agent profile precedence
• export RuntimeToolSelectionProfile from the package entrypoint
• document model-visible memory tools separately from memory maintenance scheduling

Why

Programmatic hosts could configure post-turn memory maintenance, but they could not control the default tools exposed to the model. As a result, disabling memory maintenance did not remove tools such as memory_checkpoint.

This change reuses Heddle's existing runtime tool-profile policy instead of adding host-specific filtering.

Impact

Existing engines keep the current default tool bundle. Hosts can now disable memory tools while retaining other defaults:

toolProfile: {
  preset: 'default',
  memoryMode: 'none',
}

A selected custom agent still owns its per-turn tool profile and overrides the engine default.

Validation

• yarn lint
• yarn build
• yarn test — 613 unit tests and 285 integration tests passed
• verified no private integration names were added to the public repository