docs(adr): ADR-026 names assessor + revisit cadence for dagre deferral (#361)

Cycle-2 follow-up from Elicit. The "UX-signal-only stop trigger" wording
was honest about being qualitative but left no named owner and no
cadence — if #361 changes hands in 18 months, "Albert de Gruyter's read
test failing" had no one accountable for running it. Names Felix Brandt
as owner, sets a hard 2027-05-01 fallback so the question can't drift
indefinitely.

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

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

@@ -147,3 +147,6 @@ auto-merge, try/catch fallback with structured log, deterministic input sort).
 - Brand-mint enforcement on SVG strokes (Leonie's "all connectors render in
   brand-navy, hierarchy comes from shape") stays a **code-review check at PR
   time**. No CI grep, no custom ESLint rule.
+- **Revisit cadence.** Re-evaluate dagre adoption on the first canonical
+  fixture refresh that hits AC3, OR by 2027-05-01 at the latest. Owner: Felix
+  Brandt.