docs: publish requirements baseline, ADR process, and a reference gate

[gvsambhu]

Publishes the requirements baseline and the ADR contribution process, and adds a CI gate for
unresolvable references. Ten commits, all documentation and one new check script — no behaviour
change.

Why

Requirements and ADR conventions existed only in uncommitted planning documents. A reader with just
this repository could not resolve a single FR-n reference — and the ADRs cite 21 of them — nor
follow the process for proposing an ADR.

What changed

docs/requirements.md (new) — 36 functional and non-functional requirements, each marked [v1]
or [v1.1] so that paths and flags named by unbuilt requirements read as declared scope rather than
broken references.

Traceability now runs one way: requirements state what the system must do and cite no ADRs; ADRs
state how and cite the requirement they satisfy. The previous FR→ADR citations had accumulated
because design decisions were cascaded back into the requirements source and left their provenance
inline, inverting the dependency.

Four requirements were rewritten rather than copied, because they were wrong:

• FR-2 said the knowledge graph is extracted by LLM analysis. FR-10 explicitly denies this and
  the README's point-of-view section contradicts it; the text predates the parsing-strategy decision.
• FR-3 said "scaffold" — the word deliberately replaced by "source" everywhere else, including
  the repository description.
• NFR-4 claimed CI runs both TypeScript and Go evaluation paths. Go is v1.1.
• FR-20 named a runs/<timestamp>/ directory that does not exist. The run manifest and
  structured logs are written into the output directory.

A revision history records the changes made during design review and closes at the first commit;
from there the file's git history is the record.

docs/adr/README.md — the ADR process, which was only fully described in an uncommitted
document. Numbering is now claimed by adding a row to the index table before any ADR file exists;
because that table is one file with one row per number, two people claiming the same number produce
a merge conflict, so uniqueness is serialised by merge rather than by convention. Also adds the
status lifecycle, the acceptance criteria a reviewer applies, and the areas that do not accept
outside proposals.

CONTRIBUTING.md — a "Before you start" section. The file previously opened directly on commit
conventions, so a reader arriving with an idea would have discovered the reservation requirement and
the closed areas only by having work declined. Also simplifies the AI attribution trailer and points
ADR guidance at docs/adr/.

scripts/check_no_workspace_refs.py (new) — fails on markdown links whose target does not exist,
and on references to private sibling directories that are not part of this repository. Wired into
pre-commit and the CI lint job. It found two live defects on its first run, both fixed here:

• ADR-001 linked its code sketches as a relative link to a file that was never committed at any
  path — a clickable 404 since that ADR's first commit. The sketches are now inlined.
• docs/manifest-versions.md linked ADR-017-eval-framework.md; the file is
  ADR-017-evaluation-framework.md.

Also fixed — a wrong hook count in ADR-023's D-023-1 amendment (corrected in place with a dated
errata note; the decision and its Confirmation were never affected), a CI comment describing a lint
step that does not exist, and a test docstring citing paths outside this repository.

Verification

All six CI jobs green: Lint, Unit, Integration (external), both Eval corpora, Cross-corpus Report.
Locally: ruff check, ruff format --check (209 files), mypy (205 source files), and the new
reference gate all clean.