SAG-7 | Change ASCII art banner color from green to blue

[yonbek]

Context

The cx CLI displays a Unicode block-art "CX" logo before help text. It was rendered with a mint→emerald green gradient. This changes it to blue (sky→royal) as requested in SAG-7.

Linked Issues

SAG-7 — Change color of ascii art in cli help text to blue

Design

All banner rendering lives in a single file: src/banner.rs. The file contains three color sites:

1. gradient_line() — applies a per-row truecolor gradient across the 6-line logo.
2. Tagline line — a single truecolor() call below the logo.
3. Separator line — a single truecolor() call for the ─ rule.

The change retunes only the RGB values at all three sites; the centering, terminal-width detection, NO_COLOR gate, TTY gate, and agent-mode suppression logic are completely untouched.

Key Decisions

• All three color sites changed together. Leaving the tagline/separator green while the logo turned blue would produce a visually incoherent banner. They are trivially separable if product/design later wants to revert just the supporting elements.
• Gradient approach kept. The existing top→bottom gradient interpolation is retained; only the start/end RGB values change. This preserves the visual depth effect.
• Chosen palette: sky blue #4FC3FF (top) → royal blue #1E5BCC (bottom). Legible on both dark and light terminal backgrounds; not so light that it washes out on white, not so dark that it vanishes on black.

Changes

• src/banner.rs — gradient_line: RGB math changed from mint→emerald green to sky→royal blue gradient.
• src/banner.rs — tagline: truecolor(0, 170, 110) → truecolor(60, 140, 220) (mid blue).
• src/banner.rs — separator: truecolor(0, 90, 60) → truecolor(20, 60, 140) (deep blue).
• Updated inline comment to describe the new color range.

Testing

• cargo fmt --check — passed, no formatting changes needed.
• cargo clippy --locked -- -D warnings — passed, no warnings.
• cargo test --locked — 30 tests passed, 0 failed (no banner snapshot tests exist).
• Manual: cargo run -- --help visually confirmed sky-blue logo with blue tagline and separator.

Risks & Rollout

N/A — purely cosmetic change to terminal color output. Gated by the existing should_show() check (TTY-only, respects NO_COLOR, suppressed in agent mode). No behavioral change, no API change, no config change.

Out of Scope / Follow-ups

• Changing help text colors outside the banner (clap options/usage section).
• Making the banner color configurable via env var or config file.
• Adding snapshot/golden-file tests for banner output.

🤖 Generated with Claude Code