fix(coach): compose deterministic memory facts in English by default

The deterministic fact-pattern pass fell back to German when no locale was
passed, the same de-default polarity the narrative surface just lost. Fact
text is model-facing memory, so English is the fallback for every locale
without a reviewed body; German stays for German readers.

Also correct the InsightNarrative.locale doc comment — the column holds any
shipped UI locale, not just de/en. Comment only, no SQL change.

prisma/schema.prisma

@@ -5226,7 +5226,8 @@ model InsightNarrative {
   userId           String   @map("user_id")
   /// "week" | "month".
   period           String
-  /// Resolved UI locale of the prose ("de" | "en").
+  /// Resolved UI locale of the prose — any shipped UI locale, not just de/en:
+  /// the prose is generated per locale, so the row is keyed by it.
   locale           String
   /// UTC YYYY-MM-DD boundary the narrative was generated for.
   dateKey          String   @map("date_key")

src/lib/ai/coach/facts.ts

@@ -558,7 +558,10 @@ function deterministicFactText(
   subject: string,
   locale: string | undefined,
 ): string {
-  const de = locale?.toLowerCase().startsWith("de") ?? true;
+  // German only for a German reader; every other locale — and an absent one —
+  // composes ENGLISH. The fact text is model-facing memory, so English is the
+  // fallback body; the previous `?? true` made an unknown locale German.
+  const de = locale?.toLowerCase().startsWith("de") ?? false;
   switch (kind) {
     case "allergy":
       return de