feat(dashboard): remove the hero Coach CTA

Per maintainer directive — the v1.4.34 IW-B "Frag den Coach" sparkles
button sat next to the "Hinzufügen" dropdown on the dashboard hero and
read as visual noise rather than a useful surface. Remove it; the
Coach drawer remains reachable from the /insights tree (its original
home), and the auth-shell `<CoachLaunchProvider>` + drawer mount stay
intact so any future page that wants its own opt-in CTA can call
`askCoach()` without churn.

The hook usages this leaves orphaned in `src/app/page.tsx`:
  - `useCoachLaunch` (only consumer was the CTA)
  - `useFeatureFlags` (only gate was `featureFlags.coach`)
  - `Sparkles` icon import

All drop out cleanly.

package.json

@@ -1,6 +1,6 @@
 {
   "name": "healthlog",
-  "version": "1.4.34.2",
+  "version": "1.4.34.3",
   "description": "Self-hosted personal-health-tracking PWA with Withings integration, AI insights, and doctor-report PDF export.",
   "license": "AGPL-3.0-only",
   "homepage": "https://healthlog.dev",