Make the M1 marker side-aware: M1 is the worker, M5 relays

The marker is committed, so M1's own agent reads it too. The first version
told whichever side read it to run m1-say — on M1 that meant relaying to
itself. Now each side is told its role by a one-line check for the M1-only
token file.

CLAUDE.md

@@ -2,9 +2,14 @@
 ## This project lives on M1
 
 All coding, browsing, testing and compiling for this project happens on the
-always-on **M1** server, prompted from here. This folder on the M5 is a
-**read-only git mirror** — do not edit files here and do not run builds or tests
-here.
+always-on **M1** server. First find out which side you are on — run once:
+`test -f ~/.config/claude-m1.env && echo "I am M1" || echo "I am the M5"`.
+
+**On M1 — you are the worker.** Work normally in this repo: read, edit, build,
+test and commit here. Ignore the relay notes below; they are for the other Mac.
+
+**On the M5 — this folder is a read-only git mirror.** Do not edit files here
+and do not run builds or tests here.
 
 - For **every** message about this project, run `m1-say "<the message>"` and
   show M1's reply. M1's agent does the work, on M1, and keeps going even when