Names the dated-note amendment form

[johnnyt]

Residue from campaign 030 (PR #217's direction review, findings 1 and 2),
routed to px-x5s. Docs-only; two records, both amended by addition.

What changed

docs/adr/README.md named two amendment forms - a superseding ADR, and
a later ADR replacing consequences in place - and did not name the dated
## Notes form that PR #217 introduced here. A third paragraph names it and
its constraints: appended and never rewritten, one dated subsection per
movement, citing the pull requests and beads that moved the world, zero
removed lines under docs/adr/, and no status line of its own. The README is
the index rather than a decision record, so an in-place edit is the right
shape there.

docs/adr/0017's first Note closes on "The paragraph above stands as the
record of why the exclusion existed", without naming the paragraph - and the
nearest paragraph above that sentence is the Note's own bullet list of pull
requests, not the one meant. A third dated Note names the target: the
paragraph opening "A float is outside contingently, and only until a defect
is fixed.", under "Two exclusions that are not decisions". The Note itself is
left as written, which is what the dated-note form asks for.

Provenance

• Campaign 031, fill lane D, bead px-x5s. Residue routed by the campaign 030
  conductor under D30-3 from px-dvz / PR Notes that ADR-0017's float exclusion is lifted #217 (989b149).
• Referent confirmed against 989b149's own commit message, which calls the
  target "the paragraph it supersedes ... the record of why the exclusion
  existed".
• The sibling-repo sentence was narrowed after direction review pass 1: those
  records (statifier-ui ADR-0014 through ADR-0017, opentelemetry_statifier
  ADR-0002) amend by addition under a ## Notes foot, but none uses the dated
  subsection heading this paragraph defines and two carry undated bullets, so
  the sentence now claims only that much. Verified by reading those files
  read-only; no writes were made to either repo.
• Scope: only the two files the bead names. No source, test, or changelog
  change; changelog.d/ gets no fragment because nothing user-facing moved.

Verification

• git diff against the merge base over docs/adr/ shows 28 insertions and
  0 deletions (13 in ADR-0017, 15 in the README after the cure).

• mix test test/docs_adr_links_test.exs - 7 tests, 0 failures.

• Full gate not applicable: the kit's carve-out reports "no changes under
  lib/, test/, mix.exs, mix.lock, conformance/". CI runs it regardless.

• Cure commit 4bba6b1 answers direction review pass 1's single RECORD-PROSE
  finding; a fresh cold re-review follows, scope-frozen.

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[johnnyt]

Direction review, pass 1: QUALIFIED, 1 finding (RECORD-PROSE) - the README's sibling-repo attribution overstated the dated-note form. Cured in 4bba6b1. Pass 2 (fresh cold agent, scope-frozen): UNQUALIFIED, 0 findings. Full quality gate green in CI on 4bba6b1; the repo's docs-only carve-out applies locally (no changes under lib/, test/, mix.exs, mix.lock, conformance/). Firewall scan over the diff, commit messages, PR title and body, and the bead text: clean, with a constructed positive control that fired.