Add unit tests and clean up dependencies

[bourgeoa]

Summary
Adds comprehensive test suite with 100% coverage and removes unused dependencies.

Changes
Added 22 unit tests for all pane-registry functionality
100% test coverage (statements, branches, functions, lines)
Removed unused devDependencies to reduce package size
Tests cover: registration, lookup, error handling, console logging
Test Examples
Results
✅ All 22 tests passing
✅ 100% code coverage
✅ Cleaner dependency list
✅ No breaking changes
Type: Testing + Cleanup
Version: 2.5.1

[Copilot]

Pull Request Overview

This PR restructures the pane-registry package by moving source files into a src/ directory, adding comprehensive test coverage with Jest, and updating the build/lint configuration. The main purpose is to improve code organization, testing infrastructure, and development workflow.

Key Changes:

• Moved paneRegistry.js and index.d.ts into src/ directory with updated package.json entry points
• Added Jest-based test suite with 100% code coverage and Jest configuration
• Updated ESLint configuration with separate rules for source and test files

Reviewed Changes

Copilot reviewed 5 out of 9 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
src/paneRegistry.js	Core registry implementation moved to src/ directory
src/index.d.ts	TypeScript definitions moved to src/ directory
package.json	Updated entry points, changed dependencies to peerDependencies, added Jest, removed Husky
jest.config.js	New Jest configuration for testing with coverage reporting
eslint.config.mjs	Enhanced ESLint configuration with separate rules for source and test files
tests/paneRegistry.test.js	New comprehensive test suite covering all registry functionality
TESTING.md	New documentation for testing procedures and coverage
.github/workflows/ci.yml	Removed Node.js 18.x from CI matrix

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