Lock the GET /api/analytics wire-up to the new two-axis picker with a
fixture-driven test that drives a real Postgres testcontainer + the
production handler. Four scenarios on the same Berlin day:
1. Plain default user (single source, no override) — picker passes
through; v1.4.25-today behaviour stays a regression sentinel.
2. Per-metric override (sleep: [WITHINGS, APPLE_HEALTH]) — flips
the default APPLE_HEALTH-first ladder; Withings row wins.
3. Per-device default (no user override) — Apple Watch row beats
iPhone row under same source on default ladder (watch first).
4. User flips device ladder to [phone, watch] — iPhone row wins.
Wire-up: analytics' fetchMeasurementSeriesChunked now selects
deviceType + type on every chunk so the picker can read both axes.
ChunkedRow gains two fields; all existing aggregation paths continue
to compile and the integration suite stays green (6/6 passing across
analytics-sleep-stages.test.ts + source-priority-two-axis.test.ts).
Unit tests already cover the picker's internal edge cases (45 unit
across helper + algorithm); this file is the end-to-end guard.
