fix(labs): store the catalog slug as a marker's analyte key

The matcher stored the registry entry's key, so LDL and HDL markers were
recorded as total-cholesterol. The key now names what the marker is (the
catalog slug, or a registry-only key for an analyte with no seed), and the
registry resolves ldl and hdl to the cholesterol entry for the conversion as
before. A key already written in the old form is rewritten by the same fill
step that brings a stale key in line with its name, the first time a reading
needs it. The OpenAPI descriptions say what the key is and that it follows
the marker's name and unit.

src/lib/validations/labs-ocr.ts

@@ -132,7 +132,7 @@ export interface OcrExtractedRowDto {
    */
   markerUnit: string | null;
   /**
-   * Which analyte the matched marker is (unit-conversion registry key), or null
+   * Which analyte the matched marker is (catalog slug or registry-only key), or null
    * when the marker is new or none is known. With `markerUnit` it tells the
    * review screen whether a row in another unit can be converted on Save.
    */