Add documentation for Patients With Medication Due query

Care/Clinical/patients_with_medication_due.md

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+
+# Patients With Medication Due
+
+> Count of patients whose latest 15-day medication course is overdue for renewal
+
+## Purpose
+
+Counts patients whose most recent medication request with a 15-day duration has already passed its due date. Useful for identifying how many patients may now be due for medication review, refill, or follow-up.
+
+---
+
+## Query
+
+```sql
+WITH latest_15_day_per_patient AS (
+		SELECT DISTINCT ON (emr_medicationrequest.patient_id)
+				emr_medicationrequest.patient_id,
+				emr_medicationrequest.authored_on::date AS last_prescribed_on
+		FROM emr_medicationrequest
+		WHERE  emr_medicationrequest.status != 'entered_in_error'
+			AND EXISTS (
+					SELECT 1
+					FROM jsonb_array_elements(emr_medicationrequest.dosage_instruction) AS dosage_element
+					WHERE dosage_element->'timing'->'repeat'->'bounds_duration'->>'unit' = 'd'
+						AND (dosage_element->'timing'->'repeat'->'bounds_duration'->>'value')::int = 15
+			)
+		ORDER BY emr_medicationrequest.patient_id, emr_medicationrequest.authored_on DESC
+)
+SELECT COUNT(*) AS due_patient_count
+FROM latest_15_day_per_patient
+WHERE CURRENT_DATE > (latest_15_day_per_patient.last_prescribed_on + INTERVAL '15 days')::date;
+```
+
+## Notes
+
+- **Overdue rule:** A patient is counted when `CURRENT_DATE` is strictly greater than `last_prescribed_on + 15 days`, meaning the full 15-day course has elapsed.
+- **Hardcoded duration filter:** This query only considers medication requests with a 15-day duration. If you need 7-day, 30-day, or mixed-duration tracking, adjust the JSONB filter logic.
+- **No Metabase filters:** This query currently has no Metabase variables and always evaluates against `CURRENT_DATE` at runtime.
+
+*Last updated: 2026-08-11*