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>

src/index.ts

@@ -45,6 +45,7 @@ import {
   printBaselineResults
 } from './expected-failures';
 import { createTierCheckCommand } from './tier-check';
+import { createNewSepCommand } from './new-sep';
 import packageJson from '../package.json';
 
 // Note on naming: `command` refers to which CLI command is calling this.
@@ -540,6 +541,9 @@ program
 // Tier check command
 program.addCommand(createTierCheckCommand());
 
+// New SEP scaffolding command
+program.addCommand(createNewSepCommand());
+
 // List scenarios command
 program
   .command('list')