fix(telegram): show Telegram-safe skill commands in /skills

[Zx55]

Summary

This updates the Telegram /skills output to show Telegram-safe slash command names for discovered skills.

Why

Telegram commands cannot contain hyphens, but skill names often do. cc-connect already sanitizes Telegram command registration and already resolves hyphenated and underscored names equivalently, but the /skills text still rendered the raw skill name. That made the suggested command in Telegram inconsistent with the actual slash command users could invoke.

Changes

• render skill commands in /skills using a Telegram-safe display name on Telegram
• preserve the existing display on non-Telegram platforms
• add a regression test for a hyphenated skill name such as telegram-codex-bot

Validation

• go test ./core ./platform/telegram
• manually verified in a real Telegram bot session that /skills shows /telegram_codex_bot

[chenhg5]

LGTM. Telegram-safe skill command names — sanitizeTelegramDisplayCommand strips non-alphanumeric chars and limits to lowercase alphanum. Good companion to #572's recursive discovery.

PR: #571