docs: reorganize and consolidate documentation

[nycomp]

Summary

This PR reorganizes the Campus documentation to eliminate duplication and improve clarity for both human and AI contributors.

Changes

File Structure

• Move docs/AGENTS.md → AGENTS.md (project root for better discoverability)
• Create docs/TESTING-GUIDE.md (merges content from deleted docs/test-plan.md)
• Delete docs/test-plan.md (content merged into TESTING-GUIDE.md)

Document Refactoring

Each document now has a single, well-defined purpose:

Document	Purpose
AGENTS.md	Quick reference for humans and AI agents (Poetry, run_tests.py, critical reminders)
GETTING-STARTED.md	Role-based navigation + installation only
CONTRIBUTING.md	Workflow/process (branching, PRs) + code review checklist
STYLE-GUIDE.md	Coding standards + import conventions
development-guidelines.md	Architecture patterns (starts with Storage-Model-Resources) + doc standards
TESTING-GUIDE.md	Complete testing guide with decision tree
PACKAGING.md	Build/distribution only (removed workflow content)

Key Improvements

1. No duplication - Import conventions live only in STYLE-GUIDE; doc standards only in development-guidelines; code review only in CONTRIBUTING
2. Better flow - development-guidelines now starts with foundational Storage-Model-Resources pattern
3. Accurate examples - Resources layer properly documented with actual Resource class patterns; Routes layer shows real usage
4. Test decision tree - Added to help developers choose the right test type
5. Fixes - README.md Quick Start commands corrected; broken emoji rendering in architecture.md fixed

Test Plan

• All documentation cross-references checked and updated
• No broken links within docs
• AGENTS.md moved to project root
• TESTING-GUIDE.md created from test-plan.md + tests/README.md content
• All files updated with consistent formatting

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