feat(coach): add the CoachReminder episodic-memory model

Introduce a third Coach memory type alongside facts (durable traits) and
plans (standing if-then habits): a time-anchored "bring this back later"
reminder with a due moment and a done state. The free-text note is
AES-256-GCM ciphertext via the shared Bytes codec; metric, status, the
trigger fields and the dates stay plain so the sweep and the injection
picker rank and filter without a per-row decrypt.

Migration 0196 is purely additive (status and trigger_kind are app-side
closed enums, not DB enums). Register the new note_encrypted column in the
encrypted-columns registry and the rotation script so a key rotation can
never silently skip it.

scripts/rotate-encryption-key.ts

@@ -328,6 +328,16 @@ async function main() {
     results.push(await rotateBytesColumn("CoachPlan", field, prisma.coachPlan));
   }
 
+  // ───── CoachReminder (Bytes column) ─────
+  // "noteEncrypted"
+  results.push(
+    await rotateBytesColumn(
+      "CoachReminder",
+      "noteEncrypted",
+      prisma.coachReminder,
+    ),
+  );
+
   // ───── UserHealthProfile (Bytes columns) ─────
   // "aboutMeEncrypted" "conditionsEncrypted" "allergiesEncrypted"
   // "coachFocusEncrypted" "pendingQuestionsEncrypted"