chore: point .nvmrc at 22, the version CI actually runs

.nvmrc said 20 while all six node-version declarations across the five
workflows said 22. That is the one inconsistency .nvmrc exists to prevent: its
whole job is making a local shell match CI, so `nvm use` was arranging for
contributors to reproduce bugs on a version nothing tests, and to miss ones
that only appear on 22.

CI is the authority here, not the other way round — 22 is what every workflow
has been running green on, so .nvmrc moves to meet it rather than dragging six
workflows down to 20.

The comment in checks.yml that recorded the mismatch ("Note .nvmrc says 20 —
worth reconciling, but not silently from here") is replaced rather than
deleted: it now says all six are 22 and to change them together, which is the
part that was actually worth writing down. It also said "the other two
workflows" from back when there were three.

Not touched: moving everything to 24. That is a real decision with a runtime
behind it, not a bookkeeping fix, and it does not belong in the same commit.

Author: Mikhus

.github/workflows/checks.yml

@@ -44,8 +44,10 @@ jobs:
 
       - uses: actions/setup-node@v7
         with:
-          # Matches the other two workflows. Note .nvmrc says 20 — worth
-          # reconciling, but not silently from here.
+          # 22 in all five workflows and in .nvmrc, which is the point: .nvmrc
+          # exists so a local shell runs what CI runs, and it said 20 while every
+          # workflow said 22 — so `nvm use` was arranging to reproduce bugs on a
+          # version nothing tested. Change all six together or not at all.
           node-version: 22
           cache: npm
 

.nvmrc

@@ -1 +1 @@
-20
+22