fix: address BDT merge review issues

[robotlearning123]

Summary

Follow-up fixes from PR #45 code review:

• Translate Chinese text to English in testing-principles.md
• Align L4/L5 levels: branch matrix at L4, full BDT at L5 in scoring-rubric.md
• Add missing M02 (Error without message) and L04 (boundary-1 reject) test cases
• Fix M-series ID mismatch between branch-matrices.md and test-templates.md

Test plan

• Verify no remaining Chinese text in references/
• Verify L04 and M02 test cases match branch-matrices.md definitions

🤖 Generated with Claude Code

[github-actions]

Agent Ready Scan Results

Metric	Value
Level	L1
Score	56%
Project Type	cli
Passed	true

Full Report

Agent Readiness Report

Level: L1
Score: 56%
Project Type: cli

Pillar Summary

• docs: L3 (53%)
• style: L5 (100%)
• build: L5 (89%)
• test: L4 (50%)
• security: L5 (67%)
• observability: L5 (100%)
• env: L5 (100%)
• task_discovery: L5 (67%)
• product: L5 (100%)
• agent_config: L1 (36%)
• code_quality: L2 (0%)

Failed Checks

• [L1] agent_config.gitignore_agent: File exists but does not contain required pattern: .gitignore
• [L2] agent_config.claude_commands: Found 0 files matching '.claude/commands/*.md', need at least 1
• [L2] agent_config.cursorrules: Only 0/2 alternatives passed (need 1)
• [L2] agent_config.aider_config: Only 0/3 alternatives passed (need 1)
• [L2] agent_config.copilot_config: Only 0/2 alternatives passed (need 1)
• [L2] agent_config.windsurf_rules: File not found: .windsurfrules
• [L3] agent_config.mcp_json: Only 0/2 alternatives passed (need 1)
• [L3] agent_config.claude_hooks: Found 0 files matching '.claude/hooks/*', need at least 1
• [L4] agent_config.multi_agent_support: Only 0/3 alternatives passed (need 1)
• [L4] agent_config.context_injection: Only 0/3 alternatives passed (need 1)

...and 22 more