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.

src/lib/crypto/encrypted-columns.ts

@@ -112,6 +112,8 @@ export const ENCRYPTED_COLUMNS: readonly EncryptedColumn[] = [
   { model: "CoachPlan", field: "ifCueEncrypted", kind: "bytes" },
   { model: "CoachPlan", field: "thenActionEncrypted", kind: "bytes" },
   { model: "CoachPlan", field: "targetEncrypted", kind: "bytes" },
+  // v1.22 (B2/B6) — Coach episodic reminder free-text note.
+  { model: "CoachReminder", field: "noteEncrypted", kind: "bytes" },
 
   // ───── User health profile (Bytes columns) ─────
   { model: "UserHealthProfile", field: "aboutMeEncrypted", kind: "bytes" },