fix(orb): derivePublicCommentMergeFacts's neverClosed ignores closeOwnerAuthors and admin authors

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⚠️ Definition of Done: this issue must be completed in full, in a single PR. Do not split this
work across multiple PRs, and do not defer any Deliverable below to a follow-up issue. A PR that
satisfies only some of the Deliverables, stubs a required test, or leaves a checkbox
partially-done does NOT resolve this issue and will be closed.

Context

src/queue/processors.ts:2071-2072's derivePublicCommentMergeFacts computes its neverClosed
flag using only two conditions: authorLogin === repoOwner or isProtectedAutomationAuthor.

The real close-eligibility formula used elsewhere in this same file (closeWithheldReason, lines
2226-2229) and in the canonical planner logic
(packages/loopover-engine/src/settings/agent-actions.ts:955) is:
closeEligible = isContributor || ((authorIsOwner || authorIsAdmin) && closeOwnerAuthors === true).

derivePublicCommentMergeFacts's neverClosed computation diverges from this in two ways:

• It never checks authorIsAdmin (only the repo owner), so a per-repo admin author (non-owner) is
  incorrectly NOT flagged as neverClosed, when the planner actually protects them the same as the
  owner.
• It never checks closeOwnerAuthors, so a repo with closeOwnerAuthors: true (explicitly opting
  in to closing owner-authored PRs) still shows neverClosed: true in the public comment for an
  owner-authored PR the planner can actually close.

test/unit/processors-public-comment-merge-facts.test.ts never exercises closeOwnerAuthors: true
or an admin (non-owner) author, confirming this divergence is untested.

Requirements

• Update derivePublicCommentMergeFacts's neverClosed computation to match the real
  close-eligibility formula exactly: check authorIsAdmin in addition to authorIsOwner, and
  respect closeOwnerAuthors the same way closeWithheldReason already does.

Deliverables

• neverClosed is false for an owner-authored PR when the repo has closeOwnerAuthors: true
  (currently true).
• neverClosed is true for an admin (non-owner) author when the repo does not have
  closeOwnerAuthors: true for admins (currently false).
• A new test for each of the two cases above, added to
  test/unit/processors-public-comment-merge-facts.test.ts.
• Existing tests for the currently-covered cases (contributor author, plain owner author without
  closeOwnerAuthors) continue to pass unchanged.

All Deliverables above are required in the same PR.

Test Coverage Requirements

src/** is measured by codecov/patch (99%+ target, branch-counted). The two new tests must
exercise the previously-uncovered closeOwnerAuthors: true and admin-author branches directly.

Expected Outcome

The public comment's neverClosed claim matches the real close-eligibility formula the planner
actually uses, so the public-facing text is never wrong about whether a PR could be auto-closed.

Links & Resources

• src/queue/processors.ts:2071-2072 (derivePublicCommentMergeFacts, the function to fix), :2226-2229
  (closeWithheldReason, the already-correct sibling to mirror)
• packages/loopover-engine/src/settings/agent-actions.ts:955 (the canonical formula)
• test/unit/processors-public-comment-merge-facts.test.ts (existing test file to extend)

[linear-code]

JSO-6028