tooling(pm): close H45's parent-relation silence — a pm:epic card reserved under nothing delegated (#15755)

H45 reported one shape (`pm:epic` + `pm:queue` on one card) and documented the
one it could not afford: a `pm:epic` card whose PARENT does not carry the label.
Both prices that paragraph named are now paid and declared.

- a new, named fetch class: `subIssueParentPath` — one
  `GET /repos/{owner}/{repo}/issues/{n}/parent` per `pm:epic` carrier, whose
  404 `No parent issue found` is the documented ANSWER for a parentless card
  and is counted as a probe that answered. No other sub-issues endpoint.
- a SEPARATE `pm:epic` enumeration, read last in the sweep and never folded
  into `seen`. `SEEN_LABEL_PAGES` lifts the seven pages that do feed `seen`
  out of the loop body so the exclusion is checkable rather than re-typed.
- the row files under H45, one row id and a second sentence: the registry
  keys are `H<digits>` and admit no sub-rows.
- a top-level carrier is the delegated node when EITHER free signal says so —
  it heads a subtree, or its body carries the `session_…` registration. The OR
  is what the live index forced in both directions.
- a coverage pair (`epicParentCandidates` / `epicParentProbed`) and an
  unconditional summary clause, so an unread carrier reads as UNJUDGED.

H45's first half is untouched: same predicate, same sentence, same free
population. Report-only exit semantics unchanged.


Claude-Session: https://claude.ai/code/session_019RfFHiRCSs3JXLK4cwcfox

Co-authored-by: claude <noreply@anthropic.com>

Author: claude[bot]