feat: add Discord verification bot example

[mawxcodehub]

Summary

• Adds a Discord slash-command bot example for team action verification with APort.
• Includes /aport-verify and /aport-status commands, command registration, environment configuration, and setup docs.
• Adds unit coverage for APort payload creation, decision parsing, and reply formatting.

Verification

• npm install --package-lock-only
• npm test in examples/platform-integrations/discord-bot
• node -c src/bot.js && node -c src/register-commands.js && node -c src/commands.js && node -c src/aport.js

Closes #29.