feat: config-driven architecture, install wizard, live runtime switching, usage tracking, auto-failover

Major changes:
- Config-driven adapters: all channels (Slack, Discord, Telegram, WebChat, Webhooks) controlled via config.json with enabled flags and token auto-detection, no CLI flags required
- Runtime engine field: runtime.engine selects opencode/claude from config
- Interactive install script: 8-phase setup wizard with AI runtime detection/installation, token setup, identity file personalization (personality presets), aetheel CLI command, background service (launchd/systemd)
- Live runtime switching: /engine, /model, /provider commands hot-swap the AI runtime from chat without restart, changes persisted to config.json
- Usage tracking: per-request cost extraction from Claude Code JSON output, cumulative stats via /usage command
- Auto-failover: rate limit detection on both runtimes, automatic switch to other engine on quota errors with user notification
- Chat commands work without / prefix (Slack intercepts / in channels), commands: engine, model, provider, config, usage, reload, cron, subagents, status, help
- /config set for editing config.json from chat with dotted key notation
- Security audit saved to docs/security-audit.md
- Full command reference in docs/commands.md
- Future changes doc with NanoClaw agent teams analysis
- Logo added to README and WebChat UI
- README fully rewritten with all features documented

.python-version

@@ -1 +1 @@
-3.14
+3.13