pxx 2.5.2

Added

• Goal planner runs on the roles.plan lane. pxx goal's read-only planner now
  resolves Settings.effective_role("plan") (via a testable _planner_settings helper),
  so a reasoning/planning model can decompose the goal into the task DAG while the coder
  builds it — the second consumer of the 2.5 role-lane map, matching a separate PLAN role
  (reasoning brain ≠ builder). Falls back to the coder model when [roles.plan] is unset
  (byte-identical to before). Surfaced by the clone-from-docs probe. NOTE (honesty): the
  probe's initial "planner fails greenfield with OUT_OF_SCOPE" report was a harness
  artifact — a uv run --directory invocation ran the planner in the wrong repository; a
  clean reproduce shows pxx goal works greenfield end-to-end. So this is an architectural
  enhancement (reasoning-planner support), not a bug-fix. +2 tests.