feat: init mlkem project with Verilator test framework

- sync_rtl/common/: skid_buffer, pipeline_reg, defines (valid/ready)
- sync_rtl/mod_add/: modular adder example with Verilator C++ TB
- test_framework/: Python-driven Verilator compile/sim/compare pipeline
- test_framework/modules/mod_add/: 50-vector test plan, full鏈路 PASS
- .trellis/spec/: RTL and test_framework conventions documented

.trellis/spec/backend/quality-guidelines.md

@@ -0,0 +1,51 @@
+# Quality Guidelines
+
+> Code quality standards for backend development.
+
+---
+
+## Overview
+
+<!--
+Document your project's quality standards here.
+
+Questions to answer:
+- What patterns are forbidden?
+- What linting rules do you enforce?
+- What are your testing requirements?
+- What code review standards apply?
+-->
+
+(To be filled by the team)
+
+---
+
+## Forbidden Patterns
+
+<!-- Patterns that should never be used and why -->
+
+(To be filled by the team)
+
+---
+
+## Required Patterns
+
+<!-- Patterns that must always be used -->
+
+(To be filled by the team)
+
+---
+
+## Testing Requirements
+
+<!-- What level of testing is expected -->
+
+(To be filled by the team)
+
+---
+
+## Code Review Checklist
+
+<!-- What reviewers should check -->
+
+(To be filled by the team)