chore: replace em dashes with hyphens, add no-em-dash rule to CLAUDE.md

mail/templates/layout.html.tmpl

@@ -3,7 +3,7 @@
 
   Every colour in the email system lives in this file and nowhere else, in the
   same way no component in web/, site/ or adminsite/ carries a hex. The values
-  are web/app/globals.css's tokens — an email is read before the recipient
+  are web/app/globals.css's tokens - an email is read before the recipient
   clicks through to the control plane, so the two should not look like
   different products. They are written as literal hex here because email
   clients support neither var() nor a reliable prefers-color-scheme, so the
@@ -18,7 +18,7 @@
     --ink-3      #71879f      --well       #04101f
 
   Layout is tables and inline styles throughout, which is not a stylistic
-  choice — it is the only thing Outlook renders predictably.
+  choice - it is the only thing Outlook renders predictably.
 
   A message file overrides "title", "pill" and "body"; the empty defaults below
   exist so that a message needing no pill does not have to define one.
@@ -57,7 +57,7 @@
 </p>
 {{- end -}}
 
-{{- /* well shows machine output — a licence blob, an install ID. Mirrors
+{{- /* well shows machine output - a licence blob, an install ID. Mirrors
      web/'s --well surface, the floor beneath the ground. */ -}}
 {{- define "well" -}}
 <pre style="margin:0 0 20px;padding:14px;background:#04101f;border:1px solid #1e3855;border-radius:4px;color:#9fb3ca;font-family:ui-monospace,'Cascadia Mono','SF Mono',Menlo,Consolas,monospace;font-size:12px;line-height:1.5;white-space:pre-wrap;word-break:break-all;">{{.}}</pre>