docs: AFFIRMATION.adoc overclaims 'zero escape hatches'; proof-debt.md cites a nonexistent script and CI job

[hyperpolymath]

Split out of #696, whose two substantive halves are now closed (the Idris2
duplication by #815, the Zig CI gate by the #812/#813/#696 PR). Its "For
contrast" section recorded two documentation defects that are not part of
either fix, and they should not be closed silently along with them.

1. AFFIRMATION.adoc overclaims

It states zero escape hatches. Measured across 22 .idr files: 0
assert_total, 0 postulate, 0 %hint, and 8 believe_me — 4 in comments
carrying an explicit -- hypatia: allow pragma, 4 in a deliberate scanner
fixture. None execute, so the spirit of the claim holds, but the literal claim
is false as written.

Acceptance criteria

• The claim is scoped to be exactly true — e.g. "zero escape hatches
  outside test/soundness/fixtures/" — rather than deleted or left
  absolute.
• The scoping names the fixture directory explicitly, so a future
  believe_me added outside it still contradicts the document.
• The counts quoted are re-measured at the time of the fix, not copied
  from this issue.

2. docs/proof-debt.md cites things that do not exist

• It instructs readers to run scripts/check-trusted-base.sh. No such
  script exists. Either add it or remove the instruction.
• It claims a check-trusted-base CI job enforces annotation. No such
  job exists in any workflow. Either add it or remove the claim.
• Its headline count is derived from "agent worktrees under
  .claude/worktrees/", a directory that no longer exists. Re-derive the
  count from the live tree, and state what it was derived from.
• A reader following the document end to end hits no missing file or job.

Evidence: docs/DEBT-REGISTER.md (P-1, P-2, P-3, C-4).

Note on framing: a document that instructs readers to run a nonexistent
verification script is worse than one that says nothing, because it reads as
evidence that checking happens. That is the reason to fix it rather than to
file it as cosmetic.