Reorganize PR testing docs into .claude/agents/ (#2112)

### Summary

Reorganizes the PR testing documentation into a clearer directory
structure, following the established pattern of `.claude/commands/`.

### Changes

**New structure:**
```
.claude/
├── agents/              # Agent definitions (NEW)
│   ├── pr-testing-agent.md
│   └── pr-testing-guide.md
├── commands/            # Slash commands
└── docs/               # Supporting documentation
    ├── analysis/
    ├── testing-build-scripts.md
    ├── master-health-monitoring.md
    └── ...
```

**What changed:**
- Created `.claude/agents/` directory
- Moved `pr-testing-agent.md` and `pr-testing-guide.md` from `docs/` to
`agents/`
- Updated all cross-references in both files (now point to `../docs/`
for supporting docs)
- Updated prompt examples to use new path
(`.claude/agents/pr-testing-agent.md`)

### Benefits

- **Clear separation**: Agents vs commands vs supporting documentation
- **Consistent structure**: Follows the `.claude/commands/` pattern
- **Easy to find**: Agent definitions have their own directory
- **Future-proof**: Ready for additional agents
- **No functionality changes**: Only file moves and reference updates

### Pull Request checklist

- [x] Add/update test to cover these changes - N/A, documentation
reorganization
- [x] Update documentation - Updated all cross-references
- [x] Update CHANGELOG file - N/A, documentation reorganization

<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit

* **Documentation**
* Updated PR Testing Agent and PR Testing Guide: fixed several relative
links and references to point to the new documentation locations and
corrected prompt/example references. No functional changes.

<sub>✏️ Tip: You can customize this high-level summary in your review
settings.</sub>
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

Co-authored-by: Claude <[email protected]>

Author: justin808

.claude/docs/pr-testing-agent.md renamed to .claude/agents/pr-testing-agent.md

@@ -9,10 +9,10 @@
 **See Also:**
 
 - **[PR Testing Guide](pr-testing-guide.md)** - How to use this agent with Claude Code
-- [Testing Build Scripts](testing-build-scripts.md) - Build/package testing requirements
+- [Testing Build Scripts](../docs/testing-build-scripts.md) - Build/package testing requirements
 - [CI Config Switching](../../SWITCHING_CI_CONFIGS.md) - Testing minimum vs latest dependencies
 - [Local Testing Issues](../../spec/dummy/TESTING_LOCALLY.md) - Environment-specific testing issues
-- [Master Health Monitoring](master-health-monitoring.md) - Post-merge CI monitoring
+- [Master Health Monitoring](../docs/master-health-monitoring.md) - Post-merge CI monitoring
 - [CLAUDE.md](../../CLAUDE.md) - Full development guide with CI debugging
 
 ## Agent Behavior
@@ -146,7 +146,7 @@ bundle exec rake
 
 **Why this matters:**
 
-- See [testing-build-scripts.md](testing-build-scripts.md) for real examples of silent failures
+- See [../docs/testing-build-scripts.md](../docs/testing-build-scripts.md) for real examples of silent failures
 - Build scripts run during `npm install`, `yalc publish`, and package installation
 - Failures are often SILENT in CI but break users completely
 
@@ -211,7 +211,7 @@ gh run list --workflow="Integration Tests" --branch <pr-branch> --limit 10 --jso
 # Key question: Did MY commits break it, or was it already broken?
 ```
 
-**See [testing-build-scripts.md](testing-build-scripts.md) "Before You Start: Check CI Status"**
+**See [../docs/testing-build-scripts.md](../docs/testing-build-scripts.md) "Before You Start: Check CI Status"**
 
 **Reproduce failures locally:**
 

.claude/docs/pr-testing-guide.md renamed to .claude/agents/pr-testing-guide.md

@@ -18,7 +18,7 @@ This guide shows you **how to use** the PR Testing Agent with Claude Code, inclu
 **Related Documentation:**
 
 - **[PR Testing Agent](pr-testing-agent.md)** - Core agent behavior and requirements
-- [Testing Build Scripts](testing-build-scripts.md) - Build/package testing requirements
+- [Testing Build Scripts](../docs/testing-build-scripts.md) - Build/package testing requirements
 - [CI Config Switching](../../SWITCHING_CI_CONFIGS.md) - Testing minimum vs latest dependencies
 - [CLAUDE.md](../../CLAUDE.md) - Full development guide
 
@@ -68,7 +68,7 @@ This guide shows you **how to use** the PR Testing Agent with Claude Code, inclu
 **The easiest way to use this agent with Claude Code is to explicitly reference it in your prompts:**
 
 ```
-"Use the PR Testing Agent from .claude/docs/pr-testing-agent.md to validate my testing"
+"Use the PR Testing Agent from .claude/agents/pr-testing-agent.md to validate my testing"
 
 "I changed package.json. According to PR Testing Agent Section 3, what testing is required?"
 
@@ -334,7 +334,7 @@ pbpaste | bin/ci-run-failed-specs
 
 **The PR Testing Agent guidelines are automatically available when:**
 
-- You reference `.claude/docs/pr-testing-agent.md` in prompts
+- You reference `.claude/agents/pr-testing-agent.md` in prompts
 - You mention "PR Testing Agent" or "testing checklist"
 - You ask about testing requirements for specific file types
 - CLAUDE.md is loaded (which references this documentation)
@@ -686,8 +686,8 @@ gh pr view --json statusCheckRollup
 
 **Reference documentation:**
 
-- Testing build scripts: [testing-build-scripts.md](testing-build-scripts.md)
+- Testing build scripts: [../docs/testing-build-scripts.md](../docs/testing-build-scripts.md)
 - CI debugging: [CLAUDE.md](../../CLAUDE.md) "Replicating CI Failures Locally"
 - Config switching: [SWITCHING_CI_CONFIGS.md](../../SWITCHING_CI_CONFIGS.md)
 - Local testing issues: [spec/dummy/TESTING_LOCALLY.md](../../spec/dummy/TESTING_LOCALLY.md)
-- Master health: [master-health-monitoring.md](master-health-monitoring.md)
+- Master health: [../docs/master-health-monitoring.md](../docs/master-health-monitoring.md)