Empty subpackage skeleton for the realism migration: ContentClass enum
(file/email/canary content categories), Plan dataclass (frozen, with
edit-action invariant), in_work_hours window check (wrap-around
supported, fail-open on parse error), and sample_mtime for backdated
file timestamps that snap into a persona's active hours.
Stage 1 of the orchestrator+canary realism unification — no
production caller wired yet; planner.pick is a stub returning None
until stage 3.
