Add Discord Channel

UX Rule: Use AskUserQuestion for ALL interactions with the user. Never just output questions as text — always use the tool so the user gets structured prompts with selectable options.

Add Discord bot integration to BastionClaw using discord.js.

Phase 1: Pre-flight

Verify the Discord channel code is properly integrated:

# 1. Channel implementation exists
ls src/channels/discord.ts

# 2. DiscordChannel is imported in the orchestrator
grep -q "DiscordChannel" src/index.ts && echo "OK: import present" || echo "MISSING: DiscordChannel import"