feat(consumer): versioned IR manifest + drift-check (WHYNOT-WP-0003 T03-T07,T09)

Make ir/ the unit of versioned downstream consumption so consuming repos can
pin a version, inspect it, and follow changes at their own pace.

- T03 ir/manifest.json: per-version inventory + diff anchor with deterministic
  sha256-over-canonicalised-JSON hashes; no-churn generatedAt; manifest schema.
- T07 ir/INDEX.md: human-readable catalog generated by make ir.
- T04 .whynot-design.lock sync-point format + lock schema.
- T05 npx @whynot/design drift: consumer drift-check (bin entry), exit 0/2/3,
  --json/--update/--manifest/--version/--lock.
- T06 CONSUMING.md guide + examples/consumer-fixture/ runnable demo; README +
  MultiFrameworkSupport cross-links; fix README version pin (@0.3.0 not @v0.3.0).
- T09 CONSUMER_CONTRACT_PARITY.md design-only note (live-UI parity deferred).

T02 (publish) and T08 (showcase, blocked on WP-0002 T11) remain wait. Repo stays
in dev mode; no outward publish performed.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

package.json

@@ -6,6 +6,9 @@
   "type": "module",
   "main": "./src/index.js",
   "module": "./src/index.js",
+  "bin": {
+    "whynot-design": "./bin/whynot-design.mjs"
+  },
   "exports": {
     ".":                              "./src/index.js",
     "./atoms":                        "./src/elements/atoms.js",
@@ -27,10 +30,12 @@
   },
   "files": [
     "src",
+    "bin",
     "tokens",
     "ir",
     "assets",
     "adapters",
+    "CONSUMING.md",
     "SKILL.md",
     "DesignSystemIntroduction.md",
     "MultiFrameworkSupport.md",