Per-entity phrase overrides

When a trait or the platform speaks for an entity, the entity can talk back in its own voice. A phrase <key>: line in a create block overrides the text registered under that key, for this entity only. The override can carry a strategy and or variants, exactly like a define phrase:

create the garden robin
  aka robin
  scenery
  in the Aviary Corner
  states, reversible: perched, hopping

  A round little robin with one white tail feather.

  on watching it
    change it to hopping when it is perched
    phrase robin-watched
  end on

  phrase robin-watched, cycling:
    The robin cocks its head at you, entirely unimpressed.
  or
    The robin hops once, then pretends you are not there.

  phrase detail while it is hopping:
    It hops from perch to perch as you watch.

The story-wide robin-watched text (defined in define phrases) is the default; the robin's own cycling variants win whenever the robin is the one being watched. Under the hood the override registers a derived key scoped to the entity (garden-robin.robin-watched), which is also how descriptions get their keys (garden-robin.description).

The detail key is special: it appends a live detail sentence to the entity's description and requires a while condition. On ordinary overrides, while is not allowed (analysis.override-gate); use a strategy or variants instead.