Make the canonical package.json private instead of declaring MIT (closes #119)

Repositories copy package.json to get prettier, and with "license": "MIT"
each of them declared MIT whatever its own licence is. "private": true
keeps yarn from printing "No license field" and makes no licence claim.
This repository's LICENSE and README License section are unchanged.

Model: opus-5-5

TODO.md

@@ -21,6 +21,10 @@ fmt-check, and commit.
 
 # Completed Steps
 
+- 2026-10-07: The canonical `package.json` now has `"private": true` in place of
+  `"license": "MIT"` (issue 119), so a repository that copies it no longer
+  declares MIT whatever its own licence is. yarn does not print "No license
+  field" for a private package. This repository's own licence is unchanged.
 - 2026-10-06: The canonical `.gitea/workflows/check.yml` now sets
   `fetch-depth: 0` on its checkout step (issue 110), so CI fetches the history
   and tags that `git describe --tags --always` needs, and a tagged repository

package.json

@@ -1,5 +1,5 @@
 {
-  "license": "MIT",
+  "private": true,
   "devDependencies": {
     "prettier": "3.8.1"
   }