feat(insights): adopt the canonical per-metric detail template and terminology

Bring the web per-metric Insights detail pages to structural parity with
the canonical metric template: a single top-to-bottom spine, every block
self-suppressing when its data is absent.

New spine (above the chart): header (title + target gear + Coach circle)
→ intro → primary tile → Letzte Messung → stat strip; then the chart,
the range controls + period delta, the per-metric correlation card, and
the Einschätzung assessment last.

- Add the primary tile (headline value + 30-day average + an In-range
  bar shown only when the metric carries a per-metric in-target pct).
  Blood pressure keeps its richer target panel as its primary tile.
- Add the Letzte Messung card (labeled heading + last-reading date),
  reading the last-seen timestamp the slim analytics slice already
  carries — no extra fetch.
- Relocate the owning correlation onto its metric page: weight × weekday
  on Weight, mood × pulse on Pulse. The card reads the correlations
  already on the analytics payload and self-gates below the surfacing
  bar; it is now the canonical home for those relationships.
- Move the headline value, 30-day average and in-target share out of the
  target reference panel so each figure appears in exactly one place;
  the panel stays the band reference (range, status, positional bar,
  consistency strip, source). Blood pressure keeps its stitched S/D
  30-day average inline.
- Order the Einschätzung last on every page.

Terminology: adopt the canonical labels — rename the mood patterns
surface to "Was auffällt", pluralise the deviation-count card to
"Signale des Tages", and align the settings section labels to
"Über diese App" and "Quellen-Priorität". New In-range /
30-day-average / Letzte Messung strings land in all six locales.

Web charts are unchanged — Recharts and the existing chart tokens
stay; the iOS monochrome chart doctrine is not applied.

src/components/settings/__tests__/settings-shell.test.tsx

@@ -169,7 +169,9 @@ describe("<SettingsShell>", () => {
     expect(html).toContain('href="/settings/thresholds"');
     expect(html).toContain('href="/settings/sources"');
     expect(html).toContain("Targets");
-    expect(html).toContain("Sources");
+    // v1.12.0 — the source-priority entry adopts the canonical
+    // "Source priority" / "Quellen-Priorität" label (handover §5).
+    expect(html).toContain("Source priority");
   });
 
   it("resolves every section title via the i18n provider — German", () => {