feat logging: Implement LOG_LEVEL configuration option and improve logging consistency

- Add LOG_LEVEL configuration option to control logging verbosity
- Update UI to include LOG_LEVEL dropdown in settings
- Fix logging inconsistency between environment variables and config file
- Unify logging configuration to use config file settings
- Maintain separate logging systems for different purposes:
  * Server-level logs (HTTP requests, API calls) using pino in ~/.claude-code-router/logs/
  * Application-level logs (routing decisions, business logic) in ~/.claude-code-router/claude-code-router.log
- Update documentation with accurate logging system information
- Add detailed information about dual logging systems in README.md and README_zh.md
- Improve type safety and validation in ConfigProvider

Co-authored-by: qwen-cli <https://github.com/QwenLM/qwen-code>

ui/src/components/ConfigProvider.tsx

@@ -69,6 +69,7 @@ export function ConfigProvider({ children }: ConfigProviderProps) {
         // Validate the received data to ensure it has the expected structure
         const validConfig = {
           LOG: typeof data.LOG === 'boolean' ? data.LOG : false,
+          LOG_LEVEL: typeof data.LOG_LEVEL === 'string' ? data.LOG_LEVEL : 'info',
           CLAUDE_PATH: typeof data.CLAUDE_PATH === 'string' ? data.CLAUDE_PATH : '',
           HOST: typeof data.HOST === 'string' ? data.HOST : '127.0.0.1',
           PORT: typeof data.PORT === 'number' ? data.PORT : 3456,
@@ -103,6 +104,7 @@ export function ConfigProvider({ children }: ConfigProviderProps) {
           // Set default empty config when fetch fails
           setConfig({
             LOG: false,
+            LOG_LEVEL: 'info',
             CLAUDE_PATH: '',
             HOST: '127.0.0.1',
             PORT: 3456,