feat: Implement aishell - AI-powered shell automation tool

Implemented a generic alternative to Claude Code with the following features:

Core Implementation:
- Multi-LLM provider support (OpenAI compatible APIs)
- Function calling for direct tool execution by LLM
- Interactive REPL shell interface
- MCP server mode for Claude Desktop integration
- Shell executor with bash, read, write, list tools

Architecture:
- src/cli: Interactive REPL implementation
- src/llm: LLM provider abstraction (OpenAI compatible)
- src/shell: Shell execution engine with duct
- src/mcp: MCP server for Claude Desktop
- src/config: Configuration management

Technical Stack:
- Rust 2021 with tokio async runtime
- clap for CLI framework
- reqwest for HTTP client
- duct for shell execution
- rustyline for REPL interface

This tool integrates with aigpt to form AIOS (AI Operating System),
enabling AI-driven OS management and automation.

Based on aigpt architecture for CLI and MCP patterns.

Cargo.toml

@@ -0,0 +1,47 @@
+[package]
+name = "aishell"
+version = "0.1.0"
+edition = "2021"
+authors = ["syui"]
+description = "AI-powered shell automation tool - A generic alternative to Claude Code"
+
+[lib]
+name = "aishell"
+path = "src/lib.rs"
+
+[[bin]]
+name = "aishell"
+path = "src/main.rs"
+
+[dependencies]
+# CLI and async (following aigpt pattern)
+clap = { version = "4.5", features = ["derive"] }
+tokio = { version = "1.40", features = ["rt", "rt-multi-thread", "macros", "io-std", "process", "fs"] }
+async-trait = "0.1"
+
+# HTTP client for LLM APIs
+reqwest = { version = "0.12", features = ["json", "stream"] }
+
+# Serialization
+serde = { version = "1.0", features = ["derive"] }
+serde_json = "1.0"
+
+# Error handling
+thiserror = "1.0"
+anyhow = "1.0"
+
+# Utilities
+dirs = "5.0"
+
+# Shell execution
+duct = "0.13"
+
+# Configuration
+toml = "0.8"
+
+# Logging
+tracing = "0.1"
+tracing-subscriber = { version = "0.3", features = ["env-filter"] }
+
+# Interactive REPL
+rustyline = "14.0"