chore: scrub personal gmail from docs/configs (estate-wide sweep)

Replaced jonathan.jewell@gmail.com with j.d.a.jewell@open.ac.uk per
the hyperpolymath author-attribution rule (the gmail is banned;
j.d.a.jewell@open.ac.uk is the canonical non-Git-context address).

PLACEHOLDERS files got a generic user-old@example.com so they remain
useful as templates.

.mailmap files in this repo (if any) are intentionally left — they
are the legitimate git mechanism for remapping historical commits
authored under the old gmail to the correct open.ac.uk address.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: hyperpolymath

0-AI-MANIFEST.a2ml

@@ -41,7 +41,7 @@
     (rule "Author attribution MUST be correct"
       (always "Jonathan D.A. Jewell <j.d.a.jewell@open.ac.uk>")
       (never "hyperpolymath as author name")
-      (never "jonathan.jewell@gmail.com"))
+      (never "j.d.a.jewell@open.ac.uk"))
 
     (rule "Weak points MUST have file locations"
       (never "location: None")