feat: respect NO_COLOR and strip ANSI when piped

[codesoda]

Problem

ANSI color codes are hardcoded throughout the CLI output. Colors are emitted even when:

• stdout is piped to a file or another process
• the NO_COLOR env var is set (community standard: https://no-color.org)

What to implement

1. NO_COLOR support: when NO_COLOR is set (any value), suppress all ANSI escape sequences
2. TTY detection: when stdout is not a terminal, strip ANSI automatically
3. Apply to all output in main.rs and claude_code.rs where ANSI codes are used

Approach

Add a helper (e.g. in a small output.rs module or inline):

fn color_enabled() -> bool {
    std::io::stdout().is_terminal() && std::env::var("NO_COLOR").is_err()
}

Then gate the existing ANSI escape constants on this check.

Files to touch

• src/main.rs — version banner, test output, summary formatting
• src/claude_code.rs — provider output formatting (lines 8-28 define color constants)