Add /design round-trip and design-checker agent to the fleet

Design/branding for any user-facing repo becomes a vendor-neutral on-disk
contract — design/DESIGN.md (nine-section brief) + design/tokens.tokens.json
(W3C DTCG tokens) — that every agent reads before building UI. Claude Design
is the interchangeable cloud front-end, never a dependency.

- /design (main-thread command): inspiration-first scoping -> BRIEF.md -> user
  drives the cloud step -> distill the export back into the contract. Phase-C
  token distillation is agent-mediated because the export is inline-hardcoded
  HTML/CSS, not DTCG.
- design-checker (read-only subagent): audits a repo's UI against its own
  committed contract; says "run /design first" when none exists.
- /new-project scaffolds design/ for user-facing projects.

adapters/claude/commands/design.md

@@ -0,0 +1,25 @@
+---
+description: Design round-trip — scope a look interactively (inspiration-first), hand a well-formed brief to Claude Design in the cloud, then distill the result into the repo's durable design/ contract (DESIGN.md + DTCG tokens)
+argument-hint: [optional: the surface to design, e.g. "landing page" or "settings screen"]
+allowed-tools: Bash, Read, Edit, Write, Grep, Glob, Agent
+---
+
+Run the design round-trip for this repo's user-facing interface.
+Optional surface from me (may be empty): $ARGUMENTS
+
+Your complete orchestration guide — the `design/` folder contract, the inspiration-first
+scoping conversation, the cloud-tool hand-off runbook, and how to distill the result back
+into the repo — is at:
+
+    ~/Projects/standards/guides/design.md
+
+Read it in full first, then follow it exactly. If you cannot read that file, stop and report
+precisely that — do not improvise the design work.
+
+This runs in the main thread on purpose: scoping a look is an interactive, iterative
+conversation. Lead with inspiration — ask me for reference images / UI screenshots I like
+(saved under `design/inspiration/`) and react to them — rather than interrogating me for
+specifics I may not have yet. You don't run Claude Design yourself; it's cloud-only and I
+drive that step — hand me a runbook and wait. The repo's durable contract is
+`design/DESIGN.md` + `design/tokens.tokens.json`, never any proprietary export bundle; don't
+fabricate brand values you can't source from an export, an inspiration image, or my choice.