Add design-first workflow aligned with opencode boilerplate

- New commands: /define-design, /update-design, /generate-app (web | flutter | winui3)
- New skills: ui-design, design-tokens, platform-ui-generation
- /add-feature: check design spec before implementation (Step 3.5) and reconcile all six persistent docs after implementation (Step 8)
- /setup-project: automatic document creation with self-check checkpoints
- CLAUDE.md: document docs/design/, .claude/ configuration, and the design phase in the development process
- Enrich subagent descriptions; allowlist new skills in settings.json
- Add docs/design/README.md

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

.claude/commands/review-docs.md

@@ -4,7 +4,7 @@ description: Run a detailed document review using a subagent
 
 # Document Review
 
-Argument: document path (e.g. `/review-docs docs/product-requirements.md`)
+**Document path**: `$ARGUMENTS` (e.g. `/review-docs docs/product-requirements.md`)
 
 ## How to Run
 
@@ -26,7 +26,7 @@ Launch the doc-reviewer subagent to run the review:
 Use the Task tool to launch the doc-reviewer subagent:
 - subagent_type: "doc-reviewer"
 - description: "Document detailed review"
-- prompt: "Please review [document path] in detail.\n\nEvaluate it from the following perspectives:\n1. Completeness: Are all required items included?\n2. Specificity: Are there any ambiguous expressions?\n3. Consistency: Is it consistent with other documents?\n4. Measurability: Are success metrics measurable? (for a PRD)\n\nPlease produce a review report."
+- prompt: "Please review $ARGUMENTS in detail.\n\nEvaluate it from the following perspectives:\n1. Completeness: Are all required items included?\n2. Specificity: Are there any ambiguous expressions?\n3. Consistency: Is it consistent with other documents?\n4. Measurability: Are success metrics measurable? (for a PRD)\n\nPlease produce a review report."
 
 ### Step 3: Summarize the Review Results