docs(constitution): add Spec-Kit standards to documentation requirements

- Add Spec-Kit compliance as core documentation standard
- Require PRD creation in Phase 0 before implementation
- Define PRD location (specs/prd.md) and ownership (Product Manager)
- Establish PRD as workflow gate blocking implementation
- Include structured format requirements
- Clarify document ownership by role

Spec-Kit standards now part of agent constitution.

.claude/constitution.md

@@ -47,6 +47,11 @@
   - Record in both UTC and GMT+8 (Asia/Shanghai)
   - Format: `YYYY-MM-DD HH:MM:SS UTC` and `YYYY-MM-DD HH:MM:SS GMT+8`
   - Use system time or explicitly state "To be determined" if unknown
+- **Spec-Kit Standards**: Follow Spec-Kit documentation framework
+  - PRD (Product Requirements Document) in `specs/prd.md`
+  - Structured markdown format
+  - Product Manager owns specification documents
+  - PRD required before implementation begins
 
 ### Efficiency
 - Deliver minimal viable solutions that fully address requirements
@@ -70,6 +75,37 @@
 - Highlight key decisions and their rationale
 - Offer next steps or follow-up recommendations
 
+## Documentation Standards
+
+### Spec-Kit Compliance
+
+All projects must follow **Spec-Kit** documentation framework:
+
+1. **Requirements Phase (Phase 0)**
+   - Product Manager creates PRD before any implementation
+   - PRD location: `specs/prd.md`
+   - Must include: vision, objectives, requirements, user stories, success metrics
+
+2. **Structured Format**
+   - Use markdown with clear sections
+   - Maintain version history
+   - Link related documents
+
+3. **Ownership**
+   - Product Manager: PRD and product specifications
+   - Primary Agent: Technical documentation
+   - DevOps Engineer: Infrastructure and deployment docs
+
+4. **Workflow Gate**
+   - PRD completion blocks implementation work
+   - No coding until requirements are documented
+   - Ensures alignment before development
+
+### Time Recording
+- Dual timezone format (UTC + GMT+8)
+- Never fabricate timestamps
+- Use "TBD" for unknown dates
+
 ## Ethical Boundaries
 
 ### Security First