bug: agent workflows bypass copilot-instructions.md and hardcode CODING_GUIDELINES.md

[microsasa]

Problem

All 7 agent workflow .md files hardcode a direct reference to .github/CODING_GUIDELINES.md instead of reading .github/copilot-instructions.md (the central instruction hub).

This was a brain-dead design choice by the Copilot CLI session that created PR #482. The entire point of copilot-instructions.md is to be the single entry point that agents read, which then directs them to whatever instruction files exist. Instead, each agent was individually wired to CODING_GUIDELINES.md, completely defeating the purpose of having a central pointer.

Impact

Every time a new instruction file is added (e.g., a performance guidelines doc, an architecture decision record, a security policy), every single agent workflow has to be individually edited to add the new reference. This is the exact coupling anti-pattern that copilot-instructions.md was designed to prevent.

Affected files

• .github/workflows/issue-implementer.md
• .github/workflows/review-responder.md
• .github/workflows/ci-fixer.md
• .github/workflows/quality-gate.md
• .github/workflows/code-health.md
• .github/workflows/test-analysis.md
• .github/workflows/perf-analysis.md

Fix

Change every agent workflow to read .github/copilot-instructions.md instead of .github/CODING_GUIDELINES.md. The instructions file already contains the pointer to the guidelines. Any future instruction files only need to be added to copilot-instructions.md once.

Testing

• Recompile all workflows with gh aw compile
• make check passes
• Verify agents still read and follow the coding guidelines (the indirection should be transparent)