docs: hint --path + --extension combo for unregistered checkouts

[chubes4]

Summary

The Homeboy section in DMC's AGENTS.md described --path under Git verbs but didn't tell agents that running homeboy lint --path <repo> on an unregistered checkout also needs --extension <id>. Without it Homeboy synthesizes a component id from the path basename and fails with extension.unsupported, sending the agent on a detour through homeboy component set / homeboy extension list hints that don't apply for one-off --path probes.

This adds a single trailing sentence to the Quality: bullet so future agents reach for the working invocation directly.

Repro this avoids

```bash
homeboy lint --path /Users/chubes/Developer/studio@test-dashboard-update-checks --summary

-> error: No extension provider configured for component 'studio@test-dashboard-update-checks'

homeboy lint --path /Users/chubes/Developer/studio@test-dashboard-update-checks --extension nodejs --summary

-> works: runs npm run lint via the nodejs extension

```

Why a doc fix and not a code fix

The functional path already exists — --extension <id> is a fully working one-shot override (see Homeboy ExtensionOverrideArgs). The gap was purely discoverability in the agent prompt.

Discovery

Discovered while validating Automattic/studio#3377; the Homeboy issue was tracked at Extra-Chill/homeboy#2361 and closed as not a functional gap.

AI assistance

• AI assistance: Yes
• Tool(s): Claude Code (Sonnet 4.5)
• Used for: Locating the registered AGENTS.md section in `data-machine-code.php`, drafting the one-line addition, and writing this PR body. Chris reviewed the wording and approved.