The v1.7.2 default-ON snapshot flag makes the dashboard read every tile
from GET /api/dashboard/snapshot; the e2e build sets no opt-out var, so
the specs that only mocked the legacy cells hit the real route, got
empty summaries for the zero-measurement seed user, and timed out the
tile/chart assertions.
Add a shared, correctly-typed mock helper and wire it into the five
tile-asserting specs alongside the existing legacy mocks (kept to
protect the reversible path).
