Allow admins to set buttons to Telegram's default style with no color
override. Refactors style resolution from or-chain to explicit if/elif/else
so that 'default' does not fall through to global config or hardcoded defaults.
Add cabinet admin API for configuring button colors (primary/success/danger)
and custom emoji IDs per menu section (home, subscription, balance, referral,
support, info, admin). Styles are stored as JSON in system_settings and cached
in-process for fast resolution.
Style resolution chain: explicit param > per-section DB > global config > defaults.
Fringg