📝 docs: rename agent changelog for clarity

- Rename CHANGELOG.md to AGENT_CHANGELOG.md
- Better reflects purpose as agent contribution tracker
- Distinguishes from software changelog files
- Update all references in ADR and documentation
- Maintain consistency with AGENTS.md naming

Generated by Mistral Vibe.
Co-Authored-By: Mistral Vibe <vibe@mistral.ai>

adr/0010-agent-configuration-relationship.md

@@ -37,7 +37,7 @@ sources = [
     "${project_root}/pkg/bdd/README.md", 
     "${project_root}/.vibe/skills/bdd_testing/SKILL.md",
     "${project_root}/.vibe/skills/commit_message/SKILL.md",
-    "${project_root}/CHANGELOG.md"
+    "${project_root}/AGENT_CHANGELOG.md"
 ]
 
 # Self-improvement through documentation learning
@@ -102,7 +102,7 @@ vibe start --agent dancelessonscoachprogrammer
 1. **Before adding dependencies**: Agent asks for approval
 2. **Before architectural changes**: Agent checks ADR folder and asks
 3. **Before new features**: Agent verifies roadmap alignment
-4. **All decisions**: Documented in CHANGELOG.md
+4. **All decisions**: Documented in AGENT_CHANGELOG.md
 
 ## Workflow Constraints
 
@@ -119,7 +119,7 @@ vibe start --agent dancelessonscoachprogrammer
 
 ### Always Document
 - New architectural decisions in `adr/`
-- Feature implementations in CHANGELOG.md
+- Feature implementations in AGENT_CHANGELOG.md
 - Test scenarios in `features/`
 - API changes in AGENTS.md