feat: add new-sep scaffolding command (#272)

* feat: add new-sep scaffolding command

Related #243.

This commit adds the new-sep <NNNN> subcommand, which writes the file src/scenarios/<target>/sep-<NNNN>.yaml. This file contains the "sep", "spec_url", and "requirements" rows in the same style as sep-2164.yaml, with single quotes and two spaces. The spec source resolves in order: --spec-url → --spec-path → GitHub API against modelcontextprotocol/modelcontextprotocol (explicit --pr or title search for "SEP-NNNN").
The target directory is inferred from the spec path (`server/`, `client/`, or `basic/authorization*`); the --target flag overrides this. It refuses to overwrite without the --force flag.
Token resolution reuses the "gh auth token" fallback pattern from tier-check.

It also ships the .claude/skills/new-sep directory, which drives the CLI. It fetches the spec diff via "gh api" and extracts RFC 2119 sentences. There is a warning against regex-only matching. Bullets inherit keywords from their lead-in sentence. It rewrites the placeholder rows per the severity rules in AGENTS.md. MUST/SHALL/REQUIRED are checked for FAILURE. SHOULD is checked for WARNING. MAY/OPTIONAL are excluded.

Signed-off-by: Satoshi Ito <satoshi.ito.tf@hitachi.com>

* dropped --pr arg, list changed files, support multi-file seps w url override

* Consolidate SEP yamls into src/seps/ and tighten yaml ordering

- All sep-NNNN.yaml files now live in src/seps/ regardless of which
  scenario suite their checks run in
- Drop --target / inferTarget; output dir is fixed
- renderYaml: check rows emit `check:` first, excluded rows grouped at
  bottom with a blank-line separator
- SKILL.md: document key/row ordering, expand exclusion-confirmation step
- Move src/scenarios/server/sep-2164.yaml -> src/seps/

---------

Signed-off-by: Satoshi Ito <satoshi.ito.tf@hitachi.com>
Co-authored-by: Paul Carleton <paulc@anthropic.com>

AGENTS.md

@@ -71,6 +71,16 @@ Verify requirement levels against the SEP's **spec diff** — the change to `doc
 gh api "repos/modelcontextprotocol/modelcontextprotocol/contents/docs/specification/draft/<path>?ref=<sep-branch>" --jq '.content' | base64 -d
 ```
 
+### Adding a new SEP
+
+Scaffold the requirement-traceability YAML with:
+
+```sh
+npx @modelcontextprotocol/conformance new-sep <NNNN>
+```
+
+The command looks up PR #`<NNNN>` in `modelcontextprotocol/modelcontextprotocol` (SEP numbers are PR numbers), derives `spec_url` from the `docs/specification/draft/*.mdx` file it changes, and writes `src/seps/sep-<NNNN>.yaml` with TODO `requirements[]` rows. Use `--spec-path` or `--spec-url` to skip the lookup. The `new-sep` Claude Code skill drives the same flow end-to-end, parses the spec diff, and fills in the requirement rows.
+
 ## Examples: prove it passes and fails
 
 A new scenario should come with: