fix(homeboy): single-source homeboy_project_id and resolve real registered id

[chubes4]

Summary

• Removes the duplicate homeboy_project_id() (it lived in both lib/data-machine.sh and lib/homeboy.sh; the latter won by source order, silently shadowing the fix(homeboy): report attach-path results truthfully and resolve project id consistently #169 fix).
• The surviving definition in lib/homeboy.sh now resolves in priority: $HOMEBOY_PROJECT_ID → site-root homeboy.json → domain match against homeboy project list (the real registered id). $AGENT_SLUG and homeboy_slugify remain only as last-ditch setup-time fallbacks for not-yet-registered projects.

Why

The winning homeboy.sh copy's fallback ran homeboy_slugify on the site domain, turning extrachill.com into extrachill — not a registered project (the real one is extrachill-site). Homeboy returned {"success": false, "code": "project.not_found"}.

Latent until #169 made the attach loop parse .success instead of trusting the exit code: the now-truthful failure tripped upgrade.sh's set -e and aborted the upgrade at exit 4, right after "Attaching Homeboy components".

xtrace proof:

++ homeboy_slugify extrachill.com
+ project_id=extrachill
++ homeboy project components attach-path extrachill /var/lib/.../agents-api
+ attach_output='{ "success": false, "error": { "code": "project.not_found", "details": { "id": "extrachill" } } }'

Verification

End-to-end on a Homeboy-enabled install:

• Resolves extrachill-site; attach loop completes 45 attached, 0 failed (exit 0) instead of aborting at exit 4.
• Setup-time unregistered domain (brandnew-site.com) still slugifies to brandnew-site, preserving create-project behavior.
• Only one homeboy_project_id() definition remains (grep -rn 'homeboy_project_id()' lib/).

Fixes #170