feat(skin): add light-mode skins + skin-aware completion menus

[teknium1]

Summary

Adds two built-in light-mode skins and makes completion menu / status bar backgrounds skin-configurable. Fixes the CLI being unreadable on light terminal backgrounds.

What changed

From PR #9369 (chongweiliu):

• daylight skin — Tailwind CSS-inspired blue/slate palette for light terminals (#111827 near-black text, #2563EB blue accents)
• 6 new skin color keys: completion_menu_bg, completion_menu_current_bg, completion_menu_meta_bg, completion_menu_meta_current_bg, status_bar_bg, voice_status_bg
• Makes _DIM skin-aware in cli.py (was hardcoded \033[2m, now reads banner_dim from skin)
• Refactors _hex_to_ansi_bold() → _hex_to_ansi(bold=False) so bold is optional
• Status bar + voice status prompt_toolkit style classes
• Tests and docs

From PR #4811 (ygd58):

• warm-lightmode skin — warm brown/parchment tones for light terminals (#2C1810 dark brown text, #8B4513 saddle brown accents)
• Extended with completion menu + status bar color keys for full light-mode support

How to use

/skin daylight        # cool blue/slate
/skin warm-lightmode  # warm brown/parchment

Or in ~/.hermes/config.yaml:

display:
  skin: daylight

Test plan

• 29 skin engine tests pass (27 existing + 2 new)
• Both skins verified: dark text, light completion menus, skin-aware status bars
• Pre-existing test failures in auth/env/web_server are unrelated

Attribution

Cherry-picked from PR #9369 by @chongweiliu (original commit preserved).
Warm-lightmode skin adapted from PR #4811 by @ygd58.

Closes #9369, closes #4811. Also supersedes #5353, #8679, #8567.