fix(cli): auto-select daylight skin on light terminal backgrounds

[dwc1997]

What does this PR do?

This PR improves CLI readability on light terminal themes by auto-selecting a light-safe skin when no explicit skin is configured.
Previously, Hermes defaulted to the gold-heavy default skin, which can be hard to read on white/light backgrounds. With this change, startup now uses a best-effort light terminal detection and falls back to the built-in daylight skin automatically.
Explicit user settings are preserved: if display.skin is set, Hermes continues using that exact skin with no auto override.

Related Issue

Fixes #11300

Type of Change

• 🐛 Bug fix (non-breaking change that fixes an issue)
• ✨ New feature (non-breaking change that adds functionality)
• 🔒 Security fix
• 📝 Documentation update
• ✅ Tests (adding or improving test coverage)
• ♻️ Refactor (no behavior change)
• 🎯 New skill (bundled or hub)

Changes Made

• Updated hermes_cli/skin_engine.py:
  • Added _looks_like_light_terminal() helper
  • Updated init_skin_from_config() to:
    • respect explicit display.skin
    • otherwise default to daylight on light terminals, default otherwise
• Added regression tests in tests/hermes_cli/test_skin_engine.py:
  • light terminal env selects daylight
  • explicit display.skin still takes precedence

How to Test

1. Ensure no explicit skin is set in config (display.skin unset).
2. Run with a light terminal hint, e.g.:
   • TERM_BACKGROUND=light (or HERMES_LIGHT_TERMINAL=1)
3. Start Hermes CLI and verify active skin is daylight.
4. Set display.skin: default and verify auto-detection does not override it.

Screenshots / Logs

N/A (startup behavior + test coverage)

[alt-glitch]

Competing with #11553 and #12337 which address the same light-terminal detection for #11300 / #4807. Maintainers should pick one approach.