Replace unmaintained atty crate with std library

[AlexMikhalev]

Summary

The atty crate is unmaintained and has security advisories. We should replace it with the standard library.

Details

Advisory

• atty is unmaintained: RUSTSEC-2024-0375
• atty has unsoundness issues on Windows: RUSTSEC-2021-0145

Replacement

Use std::io::IsTerminal instead, which has been stable since Rust 1.70.

Benefits

• Removes unmaintained dependency
• Fixes potential security issues
• Uses standard library (zero maintenance)

Acceptance Criteria

• Find all usages of atty in the codebase
• Replace with std::io::IsTerminal
• Remove atty from dependencies
• Verify no regressions in terminal detection

[AlexMikhalev]

Research Complete

Found 4 direct usages of atty across 4 files:

1. crates/terraphim-session-analyzer/src/main.rs:201 - Color detection
2. crates/terraphim_agent/src/main.rs:856-862 - Interactive mode detection
3. crates/terraphim_agent/src/onboarding/wizard.rs:163 - TTY check for wizard
4. crates/terraphim_atomic_client/test_signature/src/main.rs - Output redirection detection

Replacement is straightforward with std::io::IsTerminal (stable since Rust 1.70):

• atty::is(Stream::Stdout) → std::io::stdout().is_terminal()
• atty::is(Stream::Stdin) → std::io::stdin().is_terminal()

Implementation plan created at .docs/design-issue-658-atty-replacement.md

Ready to execute the fix.

[AlexMikhalev]

Fixed in commit 271d8e8.

Replaced all usages of the unmaintained atty crate with std::io::IsTerminal from the standard library.

Files changed:

• crates/terraphim-session-analyzer/src/main.rs - Replaced atty usage + removed shim module
• crates/terraphim_agent/src/main.rs - Replaced atty in interactive mode detection
• crates/terraphim_agent/src/onboarding/wizard.rs - Replaced atty in TTY check
• crates/terraphim_agent/Cargo.toml - Removed atty dependency and updated feature flag
• crates/terraphim_atomic_client/test_signature/src/main.rs - Replaced atty usage
• crates/terraphim_atomic_client/test_signature/Cargo.toml - Removed atty dependency

The atty crate (RUSTSEC-2024-0375, RUSTSEC-2021-0145) is now completely removed from the codebase.