fix: add MANDATORY prefix to all 8 core skill descriptions

- Add MANDATORY — always active to engineering-principles, testing,
  error-handling, security, git-workflow, api-design
- Update hook output with explicit EXTREMELY_IMPORTANT instruction
- Skills now explicitly state they apply to every session

skills/engineering-principles/SKILL.md

@@ -1,6 +1,6 @@
 ---
 name: engineering-principles
-description: Foundational software engineering principles that apply across all languages, frameworks, and project types — correctness, simplicity, YAGNI, KISS, DRY, root-cause fixes, least astonishment, explicit over implicit, fail fast, professional craftsmanship, and multi-agent orchestration for complex tasks. This skill is a baseline: apply these principles to every code decision, review, and architecture discussion, regardless of language or framework. Engage proactively whenever writinLine truncated
+description: MANDATORY — always active. Foundational software engineering principles that apply to every code decision, review, and architecture discussion, regardless of language or framework. 29 principles covering correctness, simplicity, YAGNI, KISS, DRY, root-cause fixes, professionalism, never suppress lints, never assume (show evidence), and multi-agent orchestration for complex tasks. Engage proactively whenever writing, reviewing, or designing code — especially when the user's requLine truncated
 ---
 
 # Engineering Principles