docs(adr): ADR-026 cross-references findAc3Candidates() predicate (#361)

Names the JavaScript function next to the AC3 SQL probe so a future reader
of ADR-026 has a concrete code anchor for the testable predicate (Markus
cycle-3 cosmetic). The SQL remains the source-of-truth probe against live
data; the function is the capture-time + fixture-time signal.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

docs/adr/026-stammbaum-layout-in-house.md

@@ -107,6 +107,16 @@ threshold, so `packBlocks.ts` is **not** yet warranted.
           AND parent.generation IS NOT NULL
     );
   ```
+
+  The same predicate is encoded as a unit-testable JavaScript function — see
+  `findAc3Candidates()` in
+  `frontend/src/lib/person/genealogy/__fixtures__/findAc3Candidates.mjs`,
+  asserted against the committed canonical fixture by
+  `validateFixture.test.ts`, and emitted as a stderr soft-warn by
+  `frontend/scripts/capture-network-fixture.mjs` on every recapture. The SQL
+  is the source-of-truth probe against live data; the function is the
+  capture-time and fixture-time signal that the predicate's count crossed
+  zero.
 - **AC6 — Bundle-impact gate (≤ 40 kB gzipped on `/stammbaum`).** Moot under
   this ADR; reactivates only under ADR-027 (dagre adoption).
 - **AC7 — Visual regression at 320 / 768 / 1440.** `toHaveScreenshot()`