Review: ask on value milestones, not exports

The old gate needed two exports, three days of install age, one prompt per
version and 120 days between prompts. Aptabase shows only 9% of users ever
export and 5% export twice, so `Review Prompt Requested` never fired once in
19 days and the store has a single rating.

Replace the export counter with three milestones -- a fully configured system,
an opened bill of materials, a completed export -- each counted at most once
per install, and ask once two different ones are reached. Recording and asking
are now separate: milestones are booked mid-task, where StoreKit and Play drop
the request, so the ask happens from calm screens only (system overview,
export preview dismissal, share sheet dismissal).

Two fixes that made the old prompt lose its slot for good: the throttle keys
were written before checking for a foreground scene, and the export trigger
fired while the Quick Look sheet was still animating away. Both platforms now
mark the throttle only once the store API really has a review flow to show.

Add a Settings entry that links straight to the store review page. It is never
throttled, and 45% of users open Settings versus 9% who export. New analytics
event `Review Milestone Reached` makes the funnel measurable.

Existing installs keep their legacy export credit and still need a second
milestone before being asked.

android/app/src/main/res/values-de/strings.xml

@@ -259,6 +259,8 @@
     <string name="settings_units_section">Einheiten</string>
     <string name="units_metric_display">Metrisch (mm², m)</string>
     <string name="units_imperial_display">Imperial (AWG, ft)</string>
+    <string name="settings_rate_title">Cable bewerten</string>
+    <string name="settings_rate_footnote">Bewertungen helfen anderen Monteuren, Cable im Play Store zu finden.</string>
     <string name="settings_disclaimer_title">Sicherheitshinweis</string>
     <string name="settings_disclaimer_body">Diese Anwendung erstellt elektrische Berechnungen zu Schulungszwecken.</string>
     <string name="settings_disclaimer_points">• Ziehe für tatsächliche Installationen stets qualifizierte Elektriker hinzu\n• Beachte alle örtlichen Vorschriften und Normen\n• Elektroarbeiten sollten nur von zertifizierten Fachkräften ausgeführt werden\n• Diese Berechnungen berücksichtigen möglicherweise nicht alle Umgebungsfaktoren\n• Die App-Entwickler übernehmen keine Haftung für elektrische Installationen</string>