feat(labs): convert a reading into its marker's unit when the pair is known

Slice 2 of phase 3 of #1095. A reading that stated a unit other than its
marker's was refused. When the marker's analyte is known and the registry has the
pair, the three write paths now convert it instead: POST /api/labs, the OCR
commit and the document commit.

The converted value is stored at full precision in the marker's unit, with what
the report printed in the existing source_value and source_unit columns. The
report's own reference window is in the printed unit, so it is converted with the
value; otherwise the verdict would compare a converted value with an unconverted
window. A pair the registry does not have is still refused as before (the 422
now says why), as is a marker whose analyte is unknown.

The marker's key is filled the first time a reading needs it. The same scan
committed again is still a duplicate: a converted row holds the number in the
marker's unit, so the duplicate check also matches on what the report printed.
Editing the value of a converted reading clears the conversion record, because
the number is then the person's own.

The lab result DTO and the OpenAPI schemas (labs and the OCR commit) carry
converted, sourceValue and sourceUnit.

Refs #1095

docs/api/openapi.yaml

@@ -14905,11 +14905,14 @@ paths:
         "403": *a11
         "409": *a7
         "422":
-          description: Nothing was written. `meta.errorCode` = `labs.create.invalid` when the body failed validation (every issue
+          description: "Nothing was written. `meta.errorCode` = `labs.create.invalid` when the body failed validation (every issue
             under `details.issues`), or `labs.unit.mismatch` when a numeric reading states a `unit` other than the one
-            its marker is tracked in (`meta.markerUnit`, `meta.readingUnit`). A unit is compared only when one is sent;
-            with a `biomarkerId` it may be omitted and the marker's unit is then the stated one. Spelling is forgiven
-            (`mmol/l`, `ug/L` for `µg/L`); a different unit is refused, never relabelled.
+            its marker is tracked in AND the pair cannot be converted (`meta.markerUnit`, `meta.readingUnit`,
+            `meta.reason` = `unknown_analyte` | `unknown_unit` | `not_finite`). A unit is compared only when one is
+            sent; with a `biomarkerId` it may be omitted and the marker's unit is then the stated one. Spelling is
+            forgiven (`mmol/l`, `ug/L` for `µg/L`); a different unit is converted when the marker's analyte is known and
+            the pair is in the unit-conversion registry (the 201 response then carries `converted: true`), and refused
+            otherwise, never relabelled."
           content:
             application/json:
               schema:
@@ -67394,6 +67397,16 @@ components:
             - type: "null"
         unit:
           type: string
+        converted:
+          type: boolean
+        sourceValue:
+          anyOf:
+            - type: number
+            - type: "null"
+        sourceUnit:
+          anyOf:
+            - type: string
+            - type: "null"
         referenceLow:
           anyOf:
             - type: number
@@ -67446,6 +67459,9 @@ components:
         - value
         - valueText
         - unit
+        - converted
+        - sourceValue
+        - sourceUnit
         - referenceLow
         - referenceHigh
         - catalogReferenceLow
@@ -67476,8 +67492,11 @@ components:
         numbers could be read out of it). `catalogReferenceLow` / `catalogReferenceHigh` are the Biomarker band.
         `referenceOrigin` names the winner and `referenceDivergesFromCatalog` is true when the report's window and the
         catalog band state different limits — a surface showing only one of the two is showing a partial answer. The
-        client renders these values and never recomputes the range. The encrypted note is never echoed in list rows;
-        `hasNote` flags its presence and the single-resource GET returns the decrypted `note`.
+        client renders these values and never recomputes the range. `converted` is true when the stored `value` was
+        converted into the marker's `unit` from another unit; `sourceValue` and `sourceUnit` are then what the report
+        printed (full precision, round for display), and the report's own window was converted with it. A reading stored
+        as stated has `converted: false` and two nulls. The encrypted note is never echoed in list rows; `hasNote` flags
+        its presence and the single-resource GET returns the decrypted `note`.
     LabReferenceRangeOrigin:
       type: string
       enum:
@@ -67556,6 +67575,16 @@ components:
             - type: "null"
         unit:
           type: string
+        converted:
+          type: boolean
+        sourceValue:
+          anyOf:
+            - type: number
+            - type: "null"
+        sourceUnit:
+          anyOf:
+            - type: string
+            - type: "null"
         referenceLow:
           anyOf:
             - type: number
@@ -67610,6 +67639,9 @@ components:
         - value
         - valueText
         - unit
+        - converted
+        - sourceValue
+        - sourceUnit
         - referenceLow
         - referenceHigh
         - catalogReferenceLow
@@ -67820,7 +67852,8 @@ components:
                   - duplicate
                   - unit_mismatch
                 description: "`duplicate`: the row matched a live reading at commit time. `unit_mismatch`: the row states a unit other
-                  than the one its marker is tracked in, so it was not written."
+                  than the one its marker is tracked in and the pair cannot be converted, so it was not written. A pair
+                  that can be converted is written in the marker's unit and reported with `converted: true`."
             required:
               - analyte
               - reason
@@ -67867,6 +67900,16 @@ components:
             - type: "null"
         unit:
           type: string
+        converted:
+          type: boolean
+        sourceValue:
+          anyOf:
+            - type: number
+            - type: "null"
+        sourceUnit:
+          anyOf:
+            - type: string
+            - type: "null"
         referenceLow:
           anyOf:
             - type: number
@@ -67928,6 +67971,9 @@ components:
         - value
         - valueText
         - unit
+        - converted
+        - sourceValue
+        - sourceUnit
         - referenceLow
         - referenceHigh
         - catalogReferenceLow
@@ -67945,6 +67991,8 @@ components:
         - updatedAt
       additionalProperties: false
       description: A written reading. Its reference window resolves exactly as it does on `/api/labs` — see `LabResult`.
+        `converted`, `sourceValue` and `sourceUnit` say when the row's unit was converted into its marker's and what the
+        report printed.
     AiRunEnvelope:
       type: object
       properties: