bus: tester identity for PM tests (row 110, #1604)

A tester binds with a process proof from the bus's own tester-cli.mjs
when the business var bus.tester is true. It may send [mos test] messages
to a role, receive replies on the tester address and use the read verbs;
every other verb refuses. Messages store from_role tester and write no
human.input event. turnRequest() marks them as never Jason's instruction.
human.mjs is unchanged.

Candidate manifest bdaf7f476abd0b2b5095ab2f7f43e38540e6ba48ee14a02a4f4995a1469b79df
(Darkwing round 2, packet 9f1563ec1), BASE badfa52b9. Approved by Filbert
(comment 28360) and Sage (comment 28361). Sage gate rerun passed.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

packages/business/src/vars.mjs

@@ -96,6 +96,8 @@ export const REGISTRY = Object.freeze({
     return v;
   }),
   "gitea.baseUrl": def(["business"], baseUrl),
+  // On: the bus binds a tester from tester-cli.mjs for PM tests (row 110). Read at bus start.
+  "bus.tester": def(["business"], boolean, { default: false }),
 
   // Project.
   "tracker.project": def(["project"], (v, key) => requirePositiveInt(v, `variable ${key}`)),