feat(labs): record qualitative lab results

Add first-class qualitative lab findings (positive / negative / borderline
serology) alongside the existing numeric path. A LabResult is now EITHER a
numeric reading (value + unit, optional reference bounds) OR a qualitative one
(valueText, e.g. "negativ"), never both, never neither.

- schema: make `value` nullable, add `value_text`; migration 0181 is additive
  (DROP NOT NULL + ADD COLUMN), every existing numeric row is untouched.
- validation: numeric-XOR-qualitative refine on create + update; unit/bounds
  apply to the numeric path only; valueText capped at 120 chars. The single
  resource PUT rejects a cross-type edit.
- serialise: carry valueText through both DTOs; a qualitative row reports the
  neutral `unknown` range verdict (no number to classify).
- FHIR: a qualitative result emits valueCodeableConcept — SNOMED qualifier
  value for confidently-known terms (Negative 260385009, Positive 10828004,
  Not detected 260415000, Detected 260373001), text-only for borderline /
  grenzwertig and any unrecognised term. The raw text always rides .text.
- UI: a numeric/qualitative toggle in the lab form; list, history, detail,
  chart, sparkline, and the doctor-report PDF all render qualitative readings
  as their text and never plot or divide on a null value.
- i18n: new labs.form keys across all six locales.
- openapi: response carries a nullable value + valueText; regenerated.

docs/api/openapi.yaml

@@ -6081,6 +6081,10 @@ paths:
                   maxLength: 120
                 value:
                   type: number
+                valueText:
+                  type: string
+                  minLength: 1
+                  maxLength: 120
                 unit:
                   type: string
                   minLength: 1
@@ -6100,7 +6104,6 @@ paths:
                     - type: string
                       const: ""
               required:
-                - value
                 - takenAt
       responses:
         "201":
@@ -6174,6 +6177,10 @@ paths:
                   maxLength: 120
                 value:
                   type: number
+                valueText:
+                  type: string
+                  minLength: 1
+                  maxLength: 120
                 unit:
                   type: string
                   minLength: 1
@@ -18838,7 +18845,13 @@ components:
         analyte:
           type: string
         value:
-          type: number
+          anyOf:
+            - type: number
+            - type: "null"
+        valueText:
+          anyOf:
+            - type: string
+            - type: "null"
         unit:
           type: string
         referenceLow:
@@ -18867,6 +18880,7 @@ components:
         - panel
         - analyte
         - value
+        - valueText
         - unit
         - referenceLow
         - referenceHigh
@@ -18877,10 +18891,12 @@ components:
         - createdAt
         - updatedAt
       additionalProperties: false
-      description: A stored lab result. `biomarkerId` links the user-scoped catalog marker (null for legacy free-text rows);
-        when linked, `analyte` / `unit` / `referenceLow` / `referenceHigh` are RESOLVED server-side from the Biomarker —
-        the client renders them 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`.
+      description: A stored lab result. Exactly one of `value` (numeric) or `valueText` (qualitative, e.g. "negativ") is
+        non-null; `rangeStatus` is always `unknown` for a qualitative row (no number to classify). `biomarkerId` links
+        the user-scoped catalog marker (null for legacy free-text rows); when linked, `analyte` / `unit` /
+        `referenceLow` / `referenceHigh` are RESOLVED server-side from the Biomarker — the client renders them 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`.
     LabReferenceRangeStatus:
       type: string
       enum:
@@ -18941,7 +18957,13 @@ components:
         analyte:
           type: string
         value:
-          type: number
+          anyOf:
+            - type: number
+            - type: "null"
+        valueText:
+          anyOf:
+            - type: string
+            - type: "null"
         unit:
           type: string
         referenceLow:
@@ -18972,6 +18994,7 @@ components:
         - panel
         - analyte
         - value
+        - valueText
         - unit
         - referenceLow
         - referenceHigh