docs(person): clarify case-collision scope at the exact-case lookups (#731)

Review noted the "never throws" claim was overstated: the exact-case Optional
lookups still surface a NonUniqueResultException on two byte-identical
same-case rows. That is a true data anomaly out of #731's scope (ambiguous =
case-insensitive) and resolves to the opaque INTERNAL_ERROR, never a wrong
row. Record that boundary at both resolution points and in ADR-032 so the gap
is not silently assumed covered.

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

backend/src/main/java/org/raddatz/familienarchiv/person/PersonService.java

@@ -111,6 +111,9 @@ public class PersonService {
     }
 
     public Optional<Person> findByName(String firstName, String lastName) {
+        // Same scope as findOrCreateByAlias (#731): a case-collision resolves without throwing;
+        // two byte-identical same-case persons are an out-of-scope data anomaly the exact
+        // Optional below would surface as the opaque INTERNAL_ERROR, not a wrong sender.
         Optional<Person> exact = personRepository.findByFirstNameAndLastName(firstName, lastName);
         if (exact.isPresent()) return exact;
         List<Person> caseInsensitive =
@@ -136,8 +139,11 @@ public class PersonService {
         if (type == PersonType.SKIP) return null;
 
         // Aliases differing only by case (müller / Müller) are valid distinct persons, not
-        // duplicates, so resolution must never throw: exact-case first, then the lowest-id
+        // duplicates, so a CASE-COLLISION must not throw: exact-case first, then the lowest-id
         // case-insensitive sibling, then create. Mirrors the tag path — see ADR-032.
+        // Scope (#731): "ambiguous" means case-insensitive. Two BYTE-IDENTICAL same-case aliases
+        // are a true data anomaly out of scope here; the exact Optional below would surface that
+        // as the opaque INTERNAL_ERROR (never a wrong row), not silently pick one.
         Optional<Person> exact = personRepository.findByAlias(alias);
         if (exact.isPresent()) return exact.get();              // exact-case wins
         List<Person> caseInsensitive = personRepository.findAllByAliasIgnoreCase(alias);