S0308-submodule-agent-doc-budgets: bring README.md and CLAUDE.md under their doc budgets

[NSchatz]

Spec: pipeline/active/S0308-submodule-agent-doc-budgets/children/dicom.md in the cosyte umbrella.

What this does

README.md goes from 71047 to 18741 bytes and CLAUDE.md from 33825 to 11518 bytes (232 lines to
93). Whole sections move, under the headings they already had, into documentation/, and every
heading they left behind now sits above a link to the file that carries it:

left in place	moved to
## Why this exists	documentation/readme-why-this-exists.md
## API, ### Access patterns, ### Error Handling	documentation/readme-api.md
## Compatibility and its three subsections	documentation/readme-compatibility.md
## Cookbook, ### De-identify before sharing	documentation/readme-cookbook.md
## Known limitations & non-goals	documentation/readme-known-limitations.md
## Traps that cost a defect to learn	documentation/claude-traps.md

documentation/ is this repository's own home for durable documentation: CLAUDE.md already sends
relocated narrative to documentation/agent-notes.md, and scripts/check-no-internal-refs.ts
classifies the directory as agent context rather than a consumer surface.

Nothing was deleted

Every non-blank line both files carried before this change is still present, byte for byte, in the
reduced file or in a file it links to. The only edits to moved text are relative links re-based by
one directory (documentation/agent-notes.md#x becomes agent-notes.md#x, ./src/parser/warnings.ts
becomes ../src/parser/warnings.ts), plus a link to a CONTRIBUTING.md this repository does not
carry, which is now plain text rather than a link that resolves nowhere.

What stays in the README is what the house skeleton in test/docs/readme-structure.test.ts and this
repository's own prose gates pin there: why the package exists, status, install, usage, the PHI and
safety statement, the temporal declaration a de-identified object makes about its own dates, and the
two known limitations a consumer has to act on.

Evidence

• Heading reachability, run per budgeted path against the base commit: prints nothing for both
  files, so no heading the file carried is unreachable from it.
• Link resolution, run per budgeted path and over each added file: prints nothing, so every markdown
  link is repo-relative, inside this repository, and resolves.
• pnpm test: 1654 passed, 1 failed. The failure is test/scripts/phi-scan-matchers.test.ts
  timing out at 10s under full-suite load; that file passes on its own (32 passed, 23s of test
  time) and reads a throwaway README under a temporary root, never this one.
• pnpm exec vitest run test/docs test/conversion-surface.test.ts: 166 passed.
• pnpm run format:check, pnpm run check:no-emdash, pnpm run check:no-internal-refs,
  pnpm phi-scan, pnpm typecheck, pnpm lint: all OK.
• npm pack --dry-run: 11 files, unchanged, because package.json files is untouched and
  documentation/ was never in it. The published tarball differs only in the bytes of README.md.

Blast radius

Markdown only. No parser, mapping, fixture, log line or listener is touched, and no public export,
warning code or behaviour changes.