refine: Update terminology from Commands/Skills to User-invoked/Model-invoked and enhance documentation

skills/engineering/README.md

@@ -2,9 +2,9 @@
 
 Skills I use daily for code work.
 
-## Commands
+## User-invoked
 
-User-invoked entry points (`disable-model-invocation: true`).
+Reachable only when you type them (`disable-model-invocation: true`).
 
 - **[grill-with-docs](./grill-with-docs/SKILL.md)** — Grilling session that also builds your project's domain model, sharpening terminology and updating `CONTEXT.md` and ADRs inline.
 - **[triage](./triage/SKILL.md)** — Move issues through a state machine of triage roles.
@@ -15,9 +15,9 @@ User-invoked entry points (`disable-model-invocation: true`).
 - **[zoom-out](./zoom-out/SKILL.md)** — Ask the agent to zoom out a level and map the relevant modules and callers.
 - **[prototype](./prototype/SKILL.md)** — Build a throwaway prototype — a runnable terminal app for state/logic questions, or several toggleable UI variations.
 
-## Skills
+## Model-invoked
 
-Model- or user-invocable (rich trigger phrasing so the model can reach for them).
+Model- or user-reachable (rich trigger phrasing so the model can reach for them).
 
 - **[diagnosing-bugs](./diagnosing-bugs/SKILL.md)** — Disciplined diagnosis loop for hard bugs and performance regressions: reproduce → minimise → hypothesise → instrument → fix → regression-test.
 - **[tdd](./tdd/SKILL.md)** — Test-driven development with a red-green-refactor loop. Builds features or fixes bugs one vertical slice at a time.