Implement Telegram bot adapter with teloxide

[bug-ops]

Description

Telegram bot using teloxide, as an alternative channel to CLI.

Parent: #5

Branch

feat/m4/telegram-adapter

Files

• crates/zeph-channels/Cargo.toml (new crate)
• crates/zeph-channels/src/lib.rs
• crates/zeph-channels/src/telegram.rs
• Cargo.toml — add to workspace members
• src/main.rs — channel selection logic
• crates/zeph-core/src/config.rs — telegram config section

Bot Commands

• /start — welcome message
• /reset — clear conversation
• /skills — list loaded skills

Acceptance Criteria

• ZEPH_TELEGRAM_TOKEN present: Telegram bot starts
• Token absent: CLI mode
• Text messages routed through agent
• Commands implemented
• telegram.allowed_users whitelist (empty = all)
• Typing indicator while processing

Depends On

#21 (Channel trait)