Refactor API handlers organization and simplify error response handling

- Modularized handlers into dedicated packages (`gemini`, `claude`, `cli`) for better structure.
- Centralized `ErrorResponse` and `ErrorDetail` types under `handlers` package for reuse.
- Updated all handlers to utilize the shared `ErrorResponse` model.
- Introduced specialization of handler structs (`GeminiAPIHandlers`, `ClaudeCodeAPIHandlers`, `GeminiCLIAPIHandlers`) for improved clarity and separation of concerns.
- Refactored `getClient` logic with additional properties and better state management.

Refactor `translator` package by modularizing code for `claude` and `gemini`

- Moved Claude-specific logic (`PrepareClaudeRequest`, `ConvertCliToClaude`) to `translator/claude/code`.
- Moved Gemini-specific logic (`FixCLIToolResponse`) to `translator/gemini/cli` for better package structure.
- Updated affected handler imports and method references.

Add comprehensive package-level documentation across key modules

- Introduced detailed package-level documentation for core modules: `auth`, `client`, `cmd`, `handlers`, `util`, `watcher`, `config`, `translator`, and `api`.
- Enhanced code readability and maintainability by clarifying the purpose and functionality of each package.
- Aligned documentation style and tone with existing codebase conventions.

Refactor API handlers and translator modules for improved clarity and consistency

- Standardized handler struct names (`GeminiAPIHandlers`, `ClaudeCodeAPIHandlers`, `GeminiCLIAPIHandlers`, `OpenAIAPIHandlers`) and updated related comments.
- Fixed unnecessary `else` blocks in streaming logic for cleaner error handling.
- Renamed variables for better readability (`responseIdResult` to `responseIDResult`, `activationUrl` to `activationURL`, etc.).
- Addressed minor inconsistencies in API handler comments and SSE header initialization.
- Improved modularization of `claude` and `gemini` translator components.

Standardize configuration field naming for consistency across modules

- Renamed `ProxyUrl` to `ProxyURL`, `ApiKeys` to `APIKeys`, and `ConfigQuotaExceeded` to `QuotaExceeded`.
- Updated all relevant references and comments in `config`, `auth`, `api`, `util`, and `watcher`.
- Ensured consistent casing for `GlAPIKey` debug logs.

internal/config/config.go

@@ -1,3 +1,7 @@
+// Package config provides configuration management for the CLI Proxy API server.
+// It handles loading and parsing YAML configuration files, and provides structured
+// access to application settings including server port, authentication directory,
+// debug settings, proxy configuration, and API keys.
 package config
 
 import (
@@ -14,17 +18,19 @@ type Config struct {
 	AuthDir string `yaml:"auth-dir"`
 	// Debug enables or disables debug-level logging and other debug features.
 	Debug bool `yaml:"debug"`
-	// ProxyUrl is the URL of an optional proxy server to use for outbound requests.
-	ProxyUrl string `yaml:"proxy-url"`
-	// ApiKeys is a list of keys for authenticating clients to this proxy server.
-	ApiKeys []string `yaml:"api-keys"`
+	// ProxyURL is the URL of an optional proxy server to use for outbound requests.
+	ProxyURL string `yaml:"proxy-url"`
+	// APIKeys is a list of keys for authenticating clients to this proxy server.
+	APIKeys []string `yaml:"api-keys"`
 	// QuotaExceeded defines the behavior when a quota is exceeded.
-	QuotaExceeded ConfigQuotaExceeded `yaml:"quota-exceeded"`
+	QuotaExceeded QuotaExceeded `yaml:"quota-exceeded"`
 	// GlAPIKey is the API key for the generative language API.
 	GlAPIKey []string `yaml:"generative-language-api-key"`
 }
 
-type ConfigQuotaExceeded struct {
+// QuotaExceeded defines the behavior when API quota limits are exceeded.
+// It provides configuration options for automatic failover mechanisms.
+type QuotaExceeded struct {
 	// SwitchProject indicates whether to automatically switch to another project when a quota is exceeded.
 	SwitchProject bool `yaml:"switch-project"`
 	// SwitchPreviewModel indicates whether to automatically switch to a preview model when a quota is exceeded.