docs: add project specs and documentation for Modbus relay control

Initialize project documentation structure:
- Add CLAUDE.md with development guidelines and architecture principles
- Add project constitution (v1.1.0) with hexagonal architecture and SOLID principles
- Add MCP server configuration for Context7 integration

Feature specification (001-modbus-relay-control):
- Complete feature spec for web-based Modbus relay control system
- Implementation plan with TDD approach using SQLx for persistence
- Type-driven development design for domain types
- Technical decisions document (SQLx over rusqlite, SQLite persistence)
- Detailed task breakdown (94 tasks across 8 phases)
- Specification templates for future features

Documentation:
- Modbus POE ETH Relay hardware documentation
- Modbus Application Protocol specification (PDF)

Project uses SQLx for compile-time verified SQL queries, aligned with
type-driven development principles.

specs/templates/spec-checklist.md

@@ -0,0 +1,34 @@
+# Specification Quality Checklist: [FEATURE NAME]
+      
+**Purpose**: Validate specification completeness and quality before proceeding to planning
+**Created**: [DATE]
+**Feature**: [Link to spec.md]
+
+## Content Quality
+
+- [ ] No implementation details (languages, frameworks, APIs)
+- [ ] Focused on user value and business needs
+- [ ] Written for non-technical stakeholders
+- [ ] All mandatory sections completed
+
+## Requirement Completeness
+
+- [ ] No [NEEDS CLARIFICATION] markers remain
+- [ ] Requirements are testable and unambiguous
+- [ ] Success criteria are measurable
+- [ ] Success criteria are technology-agnostic (no implementation details)
+- [ ] All acceptance scenarios are defined
+- [ ] Edge cases are identified
+- [ ] Scope is clearly bounded
+- [ ] Dependencies and assumptions identified
+
+## Feature Readiness
+
+- [ ] All functional requirements have clear acceptance criteria
+- [ ] User scenarios cover primary flows
+- [ ] Feature meets measurable outcomes defined in Success Criteria
+- [ ] No implementation details leak into specification
+
+## Notes
+
+- Items marked incomplete require spec updates before `/sdd:01-specify` or `/sdd:01-plan`