fix(tui): preserve readable skins across appearance modes

[tzedekr]

Summary

• Preserve the Hermes TUI look while making skins readable across light and dark terminal appearance modes
• Add contrast-safe skin/theme merging for terminal, status bar, and completion-menu colors
• Harden theme tests for light/dark detection, invalid colors, status backgrounds, and completion palette behavior

Verification

• npm --prefix ui-tui run lint: passed with 0 errors, 13 warnings
• COLORFGBG='0;15' npm --prefix ui-tui run test -- --run src/tests/theme.test.ts: 37 tests passed
• env -u COLORFGBG npm --prefix ui-tui run test: 49 files, 423 tests passed
• npm --prefix ui-tui run type-check: passed
• npm --prefix ui-tui run build: passed, compiled 112 files
• Claude Code Review: PASS

[teknium1]

Thanks for this contribution, @tzedekr! After reviewing current main, the core fix this PR implements is already covered by subsequent commits.

This is an automated hermes-sweeper review.

• The normalizeThemeForAnsiLightTerminal() function and its application inside fromSkin() landed via PR fix(tui): normalize legacy Terminal.app colors #17695 (commit 4cc6da84a, 2026-04-29): ui-tui/src/theme.ts lines 478–496 and 526.
• Light-terminal auto-detection improvements and the accompanying test hardening for COLORFGBG, HERMES_TUI_THEME, Apple_Terminal, and truecolor passthrough landed via PR feat(tui): expand light-terminal auto-detection (HERMES_TUI_THEME, background hex) #17113 (commit 258efb257, 2026-04-28).
• The ANSI color math constants (ANSI_LIGHT_MAX_LUMINANCE, ANSI_MUTED_BUCKET, ANSI_NORMALIZED_FOREGROUNDS, etc.) are all present at lines 80–100 of the current theme.ts.
• The PR is currently marked CONFLICTING against main due to these overlapping changes.

The underlying problem is fixed on main. Closing as implemented.