feat(cliproxy): add user-defined CLIProxy variants

Allow users to create custom profile names that route through CLIProxy
providers with different model configurations.

Config example:
{
  "cliproxy": {
    "flash": { "provider": "gemini", "settings": "~/.ccs/gemini-flash.settings.json" },
    "pro": { "provider": "gemini", "settings": "~/.ccs/gemini-pro.settings.json" }
  }
}

Usage: ccs flash "quick task" or ccs pro "complex analysis"

Changes:
- Add CLIProxyVariantConfig types to src/types/config.ts
- Update profile-detector to check config.cliproxy section (Priority 1)
- Pass customSettingsPath through executor chain
- Update getEffectiveEnvVars to support custom settings path
- Document feature in README.md and CLAUDE.md
- Bump version to 5.0.2

package.json

@@ -1,6 +1,6 @@
 {
   "name": "@kaitranntt/ccs",
-  "version": "5.0.1",
+  "version": "5.0.2",
   "description": "Claude Code Switch - Instant profile switching between Claude Sonnet 4.5 and GLM 4.6",
   "keywords": [
     "cli",