Documented Claude Code Discord channel setup for WiderWings Agents

Updated widerwings-agent-infra with a repeatable MacBook setup for Claude Code in Discord. Key lesson: after /discord:access pair <code> and /discord:access policy allowlist, DMs work but project channels still require /discord:access group add <channelId>. If Claude responds to DMs but ignores #agent-infra, check /discord:access; no groups means the channel is not allowlisted. Changes pushed in commit b2fe113 to README.md, docs/implementation-runbook.md, and scripts/bootstrap-claude-code-channel.sh.