feat(platform-checklist): carry implementation STATUS in the ledger — status: planned

An area item gains `status: planned` — a capability the North Star's definition
requires that the platform does not yet verify. The ledger could record only
what already works, so a capability gap had nowhere to live: the backlog sweep
had nothing to point a `Path:` at, and the platform's implementation status
lived in nobody's head.

`planned` relaxes exactly the three fields that cannot honestly exist before
the capability does — `since` (null, or the TARGET release), `steps` (none
until it is implementable) and `acceptance` (no oracle to consult) — and adds
one: `personas`, which is knowable the day the gap is found and is what makes
the gap readable to the next sweep.

The load-bearing half is the capability-coverage ratchet: a planned item is a
legal map target and carries ZERO coverage, so a kind whose only items are
planned is UNMAPPED. Otherwise `planned` would be the cheapest way to green an
untested kind and the ratchet would measure intentions instead of tests. Both
directions are pinned on fixtures in a new self-test battery, because the live
ledger carries zero planned items and cannot tell a working rule from a
deleted one.

Claude-Session: https://claude.ai/code/session_01AmH9bKvGoLjiY86Q4Z3og2
Co-authored-by: Claude <noreply@anthropic.com>

Author: claude