feat(mental-health): measure screener change against the meaningful-change threshold

The assessments list now carries, per PHQ-9, GAD-7 and WHO-5, the latest
total against the previous and the first administration, classified
against the change studies treat as meaningful: 5 points on the PHQ-9,
4 on the GAD-7, 10 on the WHO-5 percentage scale. A smaller change reads
as within the threshold rather than better or worse. The instrument
detail states each change and whether it reaches that size, in neutral
words. The read takes totals and dates only, never an answer.

docs/api/openapi.yaml

@@ -74922,6 +74922,11 @@ components:
           type: array
           items:
             $ref: "#/components/schemas/MentalHealthAssessment"
+        trends:
+          description: v1.44 — one per PHQ-9 / GAD-7 / WHO-5 with at least one administration. Absent on older servers.
+          type: array
+          items:
+            $ref: "#/components/schemas/MentalHealthAssessmentTrend"
       required:
         - assessments
       additionalProperties: false
@@ -74971,6 +74976,99 @@ components:
         diagnosis). `item9Flagged` is true when the PHQ-9 self-harm item was answered > 0 — the client MUST show crisis
         resources when it is. Raw per-item answers are intentionally absent from list rows; the by-id detail read
         returns them decrypted.
+    MentalHealthAssessmentTrend:
+      type: object
+      properties:
+        instrument:
+          type: string
+          enum:
+            - PHQ9
+            - GAD7
+            - WHO5
+        n:
+          type: integer
+          minimum: -9007199254740991
+          maximum: 9007199254740991
+        threshold:
+          type: number
+          description: "Meaningful-change threshold in reported points: PHQ-9 5, GAD-7 4, WHO-5 10 (0–100 scale)."
+        higherIsBetter:
+          type: boolean
+        first:
+          type: object
+          properties:
+            score:
+              type: number
+            takenAt:
+              type: string
+          required:
+            - score
+            - takenAt
+          additionalProperties: false
+        previous:
+          anyOf:
+            - type: object
+              properties:
+                score:
+                  type: number
+                takenAt:
+                  type: string
+              required:
+                - score
+                - takenAt
+              additionalProperties: false
+            - type: "null"
+        latest:
+          type: object
+          properties:
+            score:
+              type: number
+            takenAt:
+              type: string
+          required:
+            - score
+            - takenAt
+          additionalProperties: false
+        changeFromPrevious:
+          type:
+            - number
+            - "null"
+        changeFromFirst:
+          type:
+            - number
+            - "null"
+        sincePrevious:
+          anyOf:
+            - type: string
+              enum:
+                - improved
+                - worsened
+                - within_threshold
+            - type: "null"
+        sinceFirst:
+          anyOf:
+            - type: string
+              enum:
+                - improved
+                - worsened
+                - within_threshold
+            - type: "null"
+      required:
+        - instrument
+        - n
+        - threshold
+        - higherIsBetter
+        - first
+        - previous
+        - latest
+        - changeFromPrevious
+        - changeFromFirst
+        - sincePrevious
+        - sinceFirst
+      additionalProperties: false
+      description: v1.44 — the latest total against the previous and the first administration, classified against the
+        instrument's meaningful-change threshold in its own direction. A change below the threshold is
+        `within_threshold`. Server-computed over the whole history, not the page.
     CreateMentalHealthAssessmentEnvelope:
       type: object
       properties: