feat(insights): mood calendar and chart arrive together; add via the header plus

On /insights/mood the line chart used to paint first and the calendar,
whose aggregate is the slower read, pushed it down when it landed
(CLS 0.16 at 390 px on a cold load). The page now holds both on
final-height skeletons until the chart's read has settled and the
calendar's has landed, then shows them in the same frame. The calendar's
height is written in container-query units, so its box is the right size
from the first paint, in the skeleton and the painted grid alike. A
server wrapper prefetches both reads in parallel (time-boxed, skipped
under a record switch, off when SSR prefetch is off), so on a warm cache
they are in the first HTML. The route and the prefetch share
`moodInsightsWire`, so the seeded cell is the route's shape.

The "Log a mood entry" and "Take a mental-wellbeing check-in" text links
under the heading are gone. Logging is the header plus, which opens the
mood form in place; the check-in keeps its own place in the navigation.
The plus is one shared component, `SubPageAddButton`, now also behind
the measurement pages' capture link and the workouts page, which drew
its own. An audit of every Insights page found no other text add-button
of this kind; the remaining buttons are empty-state calls to action.
A sweep keeps it that way.

`e2e/v142-qol.spec.ts` covers all three surfaces of this change set.

src/__tests__/prefetch-page-caching-guard.test.ts

@@ -175,6 +175,7 @@ const PREFETCHING_ROUTES = [
   "/checkups",
   "/coach",
   "/insights",
+  "/insights/mood",
   "/insights/workouts",
   "/medications",
   "/mood",

src/__tests__/session-surface-guard.test.ts

@@ -138,6 +138,8 @@ describe("S1 — the direct session-resolution set is frozen", () => {
       "RSC prefetch of the session user's coach state, skipped under a switch",
     "app/insights/page.tsx":
       "RSC prefetch of the session user's insights, skipped under a switch",
+    "app/insights/mood/page.tsx":
+      "RSC prefetch of the session user's mood calendar and line, skipped under a switch",
     "app/insights/workouts/page.tsx":
       "RSC prefetch of the session user's workouts, skipped under a switch",
     "app/medications/page.tsx":