feat(insights): surface the same-time baseline on Today and in the grid

The rail gains a same_time_baseline kind and a server builder, which is the
growth path that type documents for itself. It speaks only when today is
actually outside the typical band: a card that reports doing exactly what you
usually do teaches people to stop reading the rail. Dismissing it is keyed by
day and metric, not by the hour, so it stays dismissed instead of coming back
every sixty minutes.

The Insights grid gains a section of four tiles, one per cumulative metric,
each honestly quiet until the history accrues.

The two-trajectory chart it needs did not exist, so DeltaSparkline gains a
second mode rather than a second chart family: the comparison curve rides the
same container, the same fixed height and the same shared y-domain as a dashed
muted line behind the live one, which is the only way the two can be read
against each other.

Six locales. The wipe and backup plans learn about the new table: the profile
cannot be rebuilt once the samples are gone, so it is carried, not derived.

docs/api/openapi.yaml

@@ -7396,6 +7396,7 @@ paths:
               - STAIR_DESCENT_SPEED_BASELINE
               - SIX_MINUTE_WALK_BAND
               - TRAJECTORY
+              - SAME_TIME_BASELINE
             description: "Derived-metric id to compute (e.g. VITALS_BASELINE, FITNESS_AGE, VASCULAR_AGE_DELTA, HRV_BALANCE, BMI,
               READINESS). Closed enum: an unknown id 422s. Metrics whose compute has not yet landed return an
               `insufficient` value with reason `not_implemented`."
@@ -27283,6 +27284,7 @@ components:
             - STAIR_DESCENT_SPEED_BASELINE
             - SIX_MINUTE_WALK_BAND
             - TRAJECTORY
+            - SAME_TIME_BASELINE
           description: Echoes the requested derived-metric id (tags the union).
         status:
           type: string
@@ -32913,6 +32915,7 @@ components:
             - milestone
             - ecg_new_recording
             - tension_window
+            - same_time_baseline
           description: Closed rail-item kind.
         itemKey:
           description: Stable dismiss identity, namespaced `<kind>:...`. Present only on the observational kinds (milestone /