docs: write the pages in neutral third person

The docs pages carried 36 attributed opinions — "Matt's own answer",
"his position is", quoted replies from the author. A page is a
technical document about a skill, so the substance of each finding
stays and the attribution goes: "the fix is a direct instruction: …",
"the split comes down to session count".

Quotes from *users* stay, anonymous as they already were — those are
evidence about the skill in the wild rather than the author's view.

Records the rule in .agents/writing-docs.md so new pages don't
reintroduce it.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

docs/engineering/ask-matt.md

@@ -49,7 +49,7 @@ Two of those are routinely got wrong, which is why the router carries the order
 
 **Isn't there just a list of the skills in the right order?**
 
-People keep asking for one in the README, and Matt's answer is that this is the list: "Use /ask-matt, that's what it's there for." A static table would say `wayfinder → to-spec → to-tickets → implement → code-review` and be wrong for most situations, because the interesting parts are the branches — is there a codebase, does the build span sessions, can this question be settled by talking. The honest cost is that the router is hand-maintained and lags the repo. `/grilling` and `/resolving-merge-conflicts` both shipped long before the router named them.
+People keep asking for one in the README. This skill is that list — it is what it exists for. A static table would say `wayfinder → to-spec → to-tickets → implement → code-review` and be wrong for most situations, because the interesting parts are the branches — is there a codebase, does the build span sessions, can this question be settled by talking. The honest cost is that the router is hand-maintained and lags the repo. `/grilling` and `/resolving-merge-conflicts` both shipped long before the router named them.
 
 **It told me half the skills aren't installed.**