feat(web): service page, manual update, jobs list and live job log (#7)

Also publishes the jobs topic on agent revoke and updates the agent
snippet to mount stacks read-write at the same path.

internal/master/webauth/auth_test.go

@@ -247,3 +247,10 @@ func TestLogout_DeletesSession(t *testing.T) {
 	assert.Equal(t, http.StatusOK, rec.Code)
 	assert.Empty(t, store.sessions)
 }
+
+func TestWithSession_RoundTrips(t *testing.T) {
+	ctx := WithSession(context.Background(), model.Session{Subject: "alice"})
+	sess, ok := SessionFrom(ctx)
+	assert.True(t, ok)
+	assert.Equal(t, "alice", sess.Subject)
+}