Add registratie wizard, BFF dashboard-view, contracts/value-objects, and architecture docs

Checkpoint of in-progress work: the registration wizard (address prefill,
DUO diploma lookup, policy questions), decision-DTO contracts, parse-don't-
validate value objects, infrastructure adapters, plus CLAUDE.md and the
architecture/ADR docs.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

public/mock/brp-address.json

@@ -0,0 +1,8 @@
+{
+  "gevonden": true,
+  "adres": {
+    "straat": "Lange Voorhout 9",
+    "postcode": "2514 EA",
+    "woonplaats": "Den Haag"
+  }
+}