docs: settle wayfinder as a situational on-ramp, not the main entry flow

The grill-led idea→ship chain stays the documented front door; wayfinder
is a situational on-ramp (greenfield / huge feature build), reserving
"new default spine" for a potential v2.

- ask-matt router: name wayfinder's concrete triggers
- grill-me / grill-with-docs: signpost up to wayfinder as the
  too-big-for-one-session on-ramp

Resolves the main-flow decision on the Skills v1.1 wayfinder map (#120).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

docs/engineering/grill-with-docs.md

@@ -20,7 +20,7 @@ The grilling **leaves a paper trail**. A plain interview sharpens your thinking
 
 You invoke this by typing `/grill-with-docs` — the agent won't reach for it on its own.
 
-Reach for it at the very start of a change, when the plan is still fuzzy and the domain language isn't settled, and you want to stress-test both before any code exists. If you only want the interview and don't need the artifacts, use [grilling](https://aihero.dev/skills-grilling); if the plan is already clear and you just need to pin down or record terminology, use [domain-modeling](https://aihero.dev/skills-domain-modeling).
+Reach for it at the very start of a change, when the plan is still fuzzy and the domain language isn't settled, and you want to stress-test both before any code exists. If you only want the interview and don't need the artifacts, use [grilling](https://aihero.dev/skills-grilling); if the plan is already clear and you just need to pin down or record terminology, use [domain-modeling](https://aihero.dev/skills-domain-modeling). And if the change is too big to hold in one session and its route is still foggy — a greenfield project, a huge feature build — start upstream with [wayfinder](https://aihero.dev/skills-wayfinder): it charts the effort as a map of decisions, then hands back to this main flow once the way is clear.
 
 ## Prerequisites
 

docs/productivity/grill-me.md

@@ -20,7 +20,7 @@ It asks **one question at a time** and waits. It never dumps a batch of question
 
 You invoke this by typing `/grill-me` — the agent won't reach for it on its own.
 
-Reach for it before you build, when a plan feels roughly right but you can sense unresolved decisions hiding in it — the moment you want the soft spots found and forced into the open. If you want that same interrogation to also leave a paper trail of ADRs and a glossary behind, use [grill-with-docs](https://aihero.dev/skills-grill-with-docs) instead.
+Reach for it before you build, when a plan feels roughly right but you can sense unresolved decisions hiding in it — the moment you want the soft spots found and forced into the open. If you want that same interrogation to also leave a paper trail of ADRs and a glossary behind, use [grill-with-docs](https://aihero.dev/skills-grill-with-docs) instead. And if the effort is too big to hold in one session and the route to the goal is still foggy — a greenfield project, a huge feature build — start further upstream with [wayfinder](https://aihero.dev/skills-wayfinder), which charts it as a map of decisions first and then merges back into this flow.
 
 ## The design tree