feat: add npm postinstall config creation and restructure test suite

Configuration Management:
- Add npm postinstall script to auto-create ~/.ccs/ directory and config files
- Create config.json with default profile mappings (glm, default)
- Create glm.settings.json template with GLM API configuration
- Ensure idempotent postinstall behavior (safe to run multiple times)
- Fix config-manager.js to handle missing config.json gracefully

Test Suite Restructure:
- Reorganize tests by installation method (native vs npm)
- Move 37 native Unix tests to tests/native/unix/
- Move Windows tests to tests/native/windows/
- Move 39 npm package tests to tests/npm/
- Move shared utilities to tests/shared/
- Add comprehensive test documentation and README
- Implement master orchestrators for backward compatibility
- Increase test coverage from 41 to 83+ tests (100% increase)
- Add mocha framework for npm tests with better assertions

New Test Commands:
- npm run test:npm (npm package tests only)
- npm run test:native (native tests only)
- npm run test:unit (unit tests only)
- npm run test:all (all tests)

Backward Compatibility:
- npm test (runs all tests)
- bash tests/edge-cases.sh (master orchestrator)
- All existing workflows unchanged

Version: 2.4.4

package.json

@@ -1,6 +1,6 @@
 {
   "name": "@kaitranntt/ccs",
-  "version": "2.4.3",
+  "version": "2.4.4",
   "description": "Claude Code Switch - Instant profile switching between Claude Sonnet 4.5 and GLM 4.6",
   "keywords": [
     "cli",