refactor(settings/telemetry): single card with full sub-config disclosure

Collapses the two telemetry cards (Frontend telemetry + Advanced) into
one card so the master toggle and its sub-config (sampling + allowed
events) read as one coherent block. The conditional disclosure now
hides the entire sub-config when telemetry is off — previously only the
sampling fieldset hid, leaving Advanced visible with no effect.

The sampling select sits in a 2-column grid with an empty filler so it
keeps a sensible width instead of stretching across the page. Both
redundant info blockquotes are gone (the master switch carries a muted
hint, and the events block has its own caption). The simplified
component drops the now-redundant samplingRowSelector and consumes a
single data-telemetry-when-enabled wrapper.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

i18n/default_de.json

@@ -76,6 +76,7 @@
   "Allow user theme": "Benutzer-Theme erlauben",
   "Allowed CORS origins": "Erlaubte CORS-Origins",
   "Allowed email domains": "Erlaubte E-Mail-Domains",
+  "Allowed events": "Erlaubte Events",
   "Allowed file types: PNG": "Erlaubte Dateitypen: PNG",
   "Allowed file types: SVG, PNG, JPG, WEBP": "Erlaubte Dateitypen: SVG, PNG, JPG, WEBP",
   "Allowed range: 1-365 days (default: 30)": "Erlaubter Bereich: 1–365 Tage (Standard: 30)",