📝 docs(lib): rename lib.md and update code block formatting

- Renamed `docs/readme/lib.md` to `docs/lib/lib.md` for better file structure.
- Updated code blocks to remove `path=null start=null` for cleaner rendering.

docs/lib/lib.md

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+# cull-gmail Library Documentation
+
+The `cull-gmail` library provides a Rust API for managing Gmail messages through the Gmail API. It enables programmatic email culling operations including authentication, message querying, filtering, and batch operations (trash/delete).
+
+## Installation
+
+Add the library to your `Cargo.toml`:
+
+```toml
+[dependencies]
+cull-gmail = "0.0.10"
+tokio = { version = "1.0", features = ["macros", "rt-multi-thread"] }
+```
+
+## Quick Start
+
+Here's a minimal example to get started:
+
+```rust
+use cull_gmail::{ClientConfig, GmailClient, Result};
+
+#[tokio::main]
+async fn main() -> Result<()> {
+    // Load configuration from file or environment
+    let config = ClientConfig::builder()
+        .with_credential_file("credential.json")
+        .build();
+    
+    // Create Gmail client and authenticate
+    let mut client = GmailClient::new_with_config(config).await?;
+    
+    // List first 10 messages
+    client.set_max_results(10);
+    client.get_messages(1).await?;
+    client.log_messages().await?;
+    
+    Ok(())
+}
+```
+
+## Core Types
+
+### GmailClient
+
+The main client for interacting with Gmail API:
+
+```rust
+use cull_gmail::{GmailClient, MessageList};
+
+// Create client with configuration
+let mut client = GmailClient::new_with_config(config).await?;
+
+// Query messages with Gmail search syntax
+client.set_query("older_than:1y label:promotions");
+client.add_labels(&["INBOX".to_string()])?;
+client.set_max_results(200);
+
+// Get messages (0 = all pages, 1 = first page only)
+client.get_messages(0).await?;
+
+// Access message data
+let messages = client.messages();
+let message_ids = client.message_ids();
+```
+
+### ClientConfig
+
+Handles authentication and configuration:
+
+```rust
+use cull_gmail::ClientConfig;
+
+// From credential file
+let config = ClientConfig::builder()
+    .with_credential_file("path/to/credential.json")
+    .with_config_path(".cull-gmail")
+    .build();
+
+// From individual OAuth2 parameters
+let config = ClientConfig::builder()
+    .with_client_id("your-client-id")
+    .with_client_secret("your-client-secret")
+    .with_auth_uri("https://accounts.google.com/o/oauth2/auth")
+    .with_token_uri("https://oauth2.googleapis.com/token")
+    .add_redirect_uri("http://localhost:8080")
+    .build();
+```
+
+### Rules and Retention Policies
+
+Define automated message lifecycle rules:
+
+```rust
+use cull_gmail::{Rules, Retention, MessageAge, EolAction};
+
+// Create a rule set
+let mut rules = Rules::new();
+
+// Add retention rules
+rules.add_rule(
+    Retention::new(MessageAge::Years(1), true),
+    Some(&"old-emails".to_string()),
+    false // false = trash, true = delete
+);
+
+rules.add_rule(
+    Retention::new(MessageAge::Months(6), true),
+    Some(&"promotions".to_string()),
+    false
+);
+
+// Save rules to file
+rules.save()?;
+
+// Load existing rules
+let loaded_rules = Rules::load()?;
+```
+
+### Message Operations
+
+Batch operations on messages:
+
+```rust
+use cull_gmail::{RuleProcessor, EolAction};
+
+// Set up rule and dry-run mode
+client.set_execute(false); // Dry run - no actual changes
+let rule = rules.get_rule(1).unwrap();
+client.set_rule(rule);
+
+// Find messages matching rule for a label
+client.find_rule_and_messages_for_label("promotions").await?;
+
+// Check what action would be performed
+if let Some(action) = client.action() {
+    match action {
+        EolAction::Trash => println!("Would move {} messages to trash", client.messages().len()),
+        EolAction::Delete => println!("Would delete {} messages permanently", client.messages().len()),
+    }
+}
+
+// Execute for real
+client.set_execute(true);
+match client.action() {
+    Some(EolAction::Trash) => client.batch_trash().await?,
+    Some(EolAction::Delete) => client.batch_delete().await?,
+    None => println!("No action specified"),
+}
+```
+
+## Configuration
+
+### OAuth2 Setup
+
+1. Create OAuth2 credentials in [Google Cloud Console](https://console.cloud.google.com/)
+2. Download the credential JSON file
+3. Configure the client:
+
+```rust
+let config = ClientConfig::builder()
+    .with_credential_file("path/to/credential.json")
+    .build();
+```
+
+### Configuration File
+
+The library supports TOML configuration files (default: `~/.cull-gmail/cull-gmail.toml`):
+
+```toml
+credentials = "credential.json"
+config_root = "~/.cull-gmail"
+rules = "rules.toml"
+execute = false
+
+# Alternative: direct OAuth2 parameters
+# client_id = "your-client-id"
+# client_secret = "your-client-secret"
+# token_uri = "https://oauth2.googleapis.com/token"
+# auth_uri = "https://accounts.google.com/o/oauth2/auth"
+```
+
+### Environment Variables
+
+Override configuration with environment variables:
+
+```bash
+export APP_CREDENTIALS="/path/to/credential.json"
+export APP_EXECUTE="true"
+export APP_CLIENT_ID="your-client-id"
+export APP_CLIENT_SECRET="your-client-secret"
+```
+
+## Error Handling
+
+The library uses a comprehensive error type:
+
+```rust
+use cull_gmail::{Error, Result};
+
+match client.get_messages(1).await {
+    Ok(_) => println!("Success!"),
+    Err(Error::NoLabelsFound) => println!("No labels found in mailbox"),
+    Err(Error::LabelNotFoundInMailbox(label)) => println!("Label '{}' not found", label),
+    Err(Error::GoogleGmail1(e)) => println!("Gmail API error: {}", e),
+    Err(e) => println!("Other error: {}", e),
+}
+```
+
+Common error types:
+- `NoLabelsFound`: Mailbox has no labels
+- `LabelNotFoundInMailbox(String)`: Specific label not found
+- `RuleNotFound(usize)`: Rule ID doesn't exist
+- `GoogleGmail1(Box<google_gmail1::Error>)`: Gmail API errors
+- `StdIO(std::io::Error)`: File I/O errors
+- `Config(config::ConfigError)`: Configuration errors
+
+## Async Runtime
+
+The library requires an async runtime (Tokio recommended):
+
+```toml
+[dependencies]
+tokio = { version = "1.0", features = ["macros", "rt-multi-thread"] }
+```
+
+```rust
+#[tokio::main]
+async fn main() -> cull_gmail::Result<()> {
+    // Your code here
+    Ok(())
+}
+```
+