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/error-handling.md

@@ -0,0 +1,51 @@
+# Error Handling
+
+> How errors are handled in this project.
+
+---
+
+## Overview
+
+<!--
+Document your project's error handling conventions here.
+
+Questions to answer:
+- What error types do you define?
+- How are errors propagated?
+- How are errors logged?
+- How are errors returned to clients?
+-->
+
+(To be filled by the team)
+
+---
+
+## Error Types
+
+<!-- Custom error classes/types -->
+
+(To be filled by the team)
+
+---
+
+## Error Handling Patterns
+
+<!-- Try-catch patterns, error propagation -->
+
+(To be filled by the team)
+
+---
+
+## API Error Responses
+
+<!-- Standard error response format -->
+
+(To be filled by the team)
+
+---
+
+## Common Mistakes
+
+<!-- Error handling mistakes your team has made -->
+
+(To be filled by the team)