feat(account): accept a third gender value

Add "OTHER" to the accepted gender values (the column is a free String, so no
migration) and surface it in the account selector. This lets a non-binary or
trans user record their gender and opt into the cycle-tracking surface through
the per-user enable flag, rather than being gated out by a binary field.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

prisma/schema.prisma

@@ -48,7 +48,7 @@ model User {
   // Profile
   heightCm    Float?    @map("height_cm")
   dateOfBirth DateTime? @map("date_of_birth")
-  gender      String?   @map("gender") // "MALE" | "FEMALE" | null = keine Angabe
+  gender      String?   @map("gender") // "MALE" | "FEMALE" | "OTHER" | null = keine Angabe
   timezone    String    @default("Europe/Berlin")
 
   // Codex OAuth (ChatGPT subscription)