capsite/toybox: routing carries no secrets

The ingress no longer reads labels from a Toybox-Labels header. A header
was no place for the webkey pattern: browsers can't set one on a
WebSocket, and the pattern puts the secret in-band anyway. A page keeps
it in its fragment, reaches the vat by public labels, and sends it in
the body of a call, which the vat checks like a swissnum.

A request still reaches a vat only by naming every label of its mount.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

toybox/test/mounts-sql.test.js

@@ -19,11 +19,11 @@ const makeDb = () => {
 
 test("a request reaches the mount whose every label it carries", () => {
 	const { mount, lookup } = makeDb();
-	mount("a", { vat: "alice", key: "s3cret" });
+	mount("a", { vat: "alice", flavor: "plain" });
 	mount("b", { vat: "bob" });
-	assert.equal(lookup({ vat: "alice", key: "s3cret", page: "2" }), "a");
+	assert.equal(lookup({ vat: "alice", flavor: "plain", page: "2" }), "a");
 	assert.equal(lookup({ vat: "alice" }), null);
-	assert.equal(lookup({ vat: "alice", key: "wrong" }), null);
+	assert.equal(lookup({ vat: "alice", flavor: "fancy" }), null);
 	assert.equal(lookup({ vat: "bob" }), "b");
 	assert.equal(lookup({}), null);
 });