Signals: an admin chooses whether the server's TypeSafe key pays for everyone (#271)

With signals_on_server set and TYPESAFE_KEY present, the judge asks Jev
about everyone's Signals on the server's key; otherwise each person turns
Signals on in Settings with a key of their own, which is now checked with
TypeSafe before it is saved. The Signals folder shows only when they are on.

The browser suite's daemon inherited the shell's TYPESAFE_KEY, so fixture
feeds were sent to the real TypeSafe to be categorised; it is blanked now,
and an empty key counts as none.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tests/page-unit.js

@@ -199,3 +199,12 @@ test('Jev is offered the icons found for each word of a Signal', () => {
   assert.deepEqual(offered('Apple'), ['brands/apple', 'solid/apple-whole']);
   assert.equal(run(`signalCounts({items: 12, unread: 1})`), '12 items · 1 unread');
 });
+
+test('Signals are everyone\'s on the server\'s key, and yours on your own once a key is saved', () => {
+  const on = me => { run(`S.me = ${JSON.stringify(me)}`); return run('signalsOn()'); };
+  assert.equal(on({ signals: 'server', typesafe_key_set: false }), true);
+  assert.equal(on({ signals: 'own', typesafe_key_set: true }), true);
+  assert.equal(on({ signals: 'own', typesafe_key_set: false }), false);
+  assert.equal(on(null), false);
+  run('S.me = null');
+});