docs: Add comprehensive documentation and examples to cargo-hammerwork CLI

- Add extensive module-level documentation to lib.rs with CLI usage patterns
- Document configuration management with loading, saving, and environment variable examples
- Add database utilities documentation with connection and migration examples
- Document display utilities with table formatting and helper function examples
- Add 21 passing documentation tests covering all major CLI functionality
- Include real-world usage examples for complete workflows
- Provide installation, basic usage, and advanced command examples
- Document error handling and configuration precedence
- Add examples for PostgreSQL and MySQL database connections

This makes docs.rs significantly more useful for users with comprehensive
examples and context for effective CLI usage.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <[email protected]>

Author: CodingAnarchy

cargo-hammerwork/src/config/mod.rs

@@ -1,15 +1,134 @@
+//! Configuration management for the Hammerwork CLI.
+//!
+//! This module handles loading, saving, and managing configuration for the CLI tool.
+//! Configuration can be loaded from multiple sources with the following precedence:
+//!
+//! 1. Environment variables (highest priority)
+//! 2. Configuration file
+//! 3. Default values (lowest priority)
+//!
+//! # Configuration File Location
+//!
+//! The configuration file is stored at platform-specific locations:
+//!
+//! - **Linux/Mac**: `~/.config/hammerwork/config.toml`
+//! - **Windows**: `%APPDATA%\hammerwork\config.toml`
+//!
+//! # Examples
+//!
+//! ## Loading Configuration
+//!
+//! ```rust,no_run
+//! use cargo_hammerwork::config::Config;
+//!
+//! // Load configuration from file and environment
+//! let config = Config::load().expect("Failed to load config");
+//!
+//! // Access configuration values
+//! if let Some(db_url) = config.get_database_url() {
+//!     println!("Database URL: {}", db_url);
+//! }
+//!
+//! println!("Default queue: {:?}", config.get_default_queue());
+//! println!("Default limit: {}", config.get_default_limit());
+//! ```
+//!
+//! ## Creating and Saving Configuration
+//!
+//! ```rust,no_run
+//! use cargo_hammerwork::config::Config;
+//!
+//! // Create a new configuration with custom values
+//! let mut config = Config::default();
+//! config.database_url = Some("postgresql://localhost/hammerwork".to_string());
+//! config.default_queue = Some("default".to_string());
+//! config.default_limit = Some(100);
+//! config.log_level = Some("debug".to_string());
+//!
+//! // Save configuration to file
+//! config.save().expect("Failed to save config");
+//! ```
+//!
+//! ## Environment Variable Override
+//!
+//! ```rust,no_run
+//! use std::env;
+//! use cargo_hammerwork::config::Config;
+//!
+//! // Set environment variables (unsafe in real code, safe for docs)
+//! unsafe {
+//!     env::set_var("DATABASE_URL", "postgresql://prod-server/hammerwork");
+//!     env::set_var("HAMMERWORK_DEFAULT_QUEUE", "high-priority");
+//!     env::set_var("HAMMERWORK_LOG_LEVEL", "warn");
+//! }
+//!
+//! // Load config - environment variables take precedence
+//! let config = Config::load().expect("Failed to load config");
+//!
+//! assert_eq!(config.get_database_url(), Some("postgresql://prod-server/hammerwork"));
+//! assert_eq!(config.get_default_queue(), Some("high-priority"));
+//! assert_eq!(config.get_log_level(), "warn");
+//! ```
+//!
+//! ## Configuration File Format
+//!
+//! The configuration file uses TOML format:
+//!
+//! ```toml
+//! database_url = "postgresql://localhost/hammerwork"
+//! default_queue = "default"
+//! default_limit = 50
+//! log_level = "info"
+//! connection_pool_size = 5
+//! ```
+//!
+//! # Environment Variables
+//!
+//! The following environment variables are supported:
+//!
+//! - `DATABASE_URL` - Database connection URL
+//! - `HAMMERWORK_DEFAULT_QUEUE` - Default queue name
+//! - `HAMMERWORK_DEFAULT_LIMIT` - Default limit for list operations
+//! - `HAMMERWORK_LOG_LEVEL` - Logging level (error, warn, info, debug, trace)
+//! - `HAMMERWORK_POOL_SIZE` - Database connection pool size
+
 use anyhow::Result;
 use serde::{Deserialize, Serialize};
 use std::env;
 use std::fs;
 use std::path::PathBuf;
 
+/// CLI configuration structure.
+///
+/// This struct holds all configuration options for the Hammerwork CLI.
+/// Fields are optional to allow partial configuration and merging from multiple sources.
+///
+/// # Examples
+///
+/// ```rust
+/// use cargo_hammerwork::config::Config;
+///
+/// // Create configuration with defaults
+/// let config = Config::default();
+/// assert_eq!(config.get_default_limit(), 50);
+/// assert_eq!(config.get_log_level(), "info");
+/// assert_eq!(config.get_connection_pool_size(), 5);
+/// ```
 #[derive(Debug, Clone, Serialize, Deserialize)]
 pub struct Config {
+    /// Database connection URL (e.g., "postgresql://localhost/hammerwork")
     pub database_url: Option<String>,
+    
+    /// Default queue name for operations
     pub default_queue: Option<String>,
+    
+    /// Default limit for list operations
     pub default_limit: Option<u32>,
+    
+    /// Log level (error, warn, info, debug, trace)
     pub log_level: Option<String>,
+    
+    /// Database connection pool size
     pub connection_pool_size: Option<u32>,
 }
 
@@ -26,6 +145,21 @@ impl Default for Config {
 }
 
 impl Config {
+    /// Load configuration from file and environment variables.
+    ///
+    /// Configuration is loaded with the following precedence:
+    /// 1. Environment variables (highest priority)
+    /// 2. Configuration file at `~/.config/hammerwork/config.toml`
+    /// 3. Default values (lowest priority)
+    ///
+    /// # Examples
+    ///
+    /// ```rust,no_run
+    /// use cargo_hammerwork::config::Config;
+    ///
+    /// let config = Config::load().expect("Failed to load configuration");
+    /// println!("Database URL: {:?}", config.database_url);
+    /// ```
     pub fn load() -> Result<Self> {
         let mut config = Self::default();
 
@@ -69,6 +203,21 @@ impl Config {
         Ok(config)
     }
 
+    /// Save configuration to file.
+    ///
+    /// The configuration is saved to the platform-specific location:
+    /// - Linux/Mac: `~/.config/hammerwork/config.toml`
+    /// - Windows: `%APPDATA%\hammerwork\config.toml`
+    ///
+    /// # Examples
+    ///
+    /// ```rust,no_run
+    /// use cargo_hammerwork::config::Config;
+    ///
+    /// let mut config = Config::default();
+    /// config.database_url = Some("postgresql://localhost/hammerwork".to_string());
+    /// config.save().expect("Failed to save configuration");
+    /// ```
     pub fn save(&self) -> Result<()> {
         let config_path = Self::config_file_path()?;