Add passkeys project: WebAuthn ceremonies, a software authenticator and the one-time-token fallback

Fourth Maven project in the repository. Registration and authentication run end to
end with no browser and no hardware key: VirtualAuthenticator emits real CBOR
attestation objects and real ES256 assertion signatures, and tools/PasskeyCeremony.java
drives the live HTTP endpoints with them.

Profiles cover userVerification REQUIRED, DIRECT attestation, a disallowed origin and
JDBC persistence. Eleven doc chapters and twelve captured transcripts under docs/passkeys
and docs/output/pk-*.txt, all regenerated by passkeys/scripts/run-all.sh.

passkeys/scripts/jdbc.sh

@@ -0,0 +1,13 @@
+#!/usr/bin/env bash
+# Credentials in a database, using the DDL that ships inside spring-security-web.
+source "$(dirname "${BASH_SOURCE[0]}")/lib.sh"
+start_app jdbc > /dev/null
+{
+  header "JDBC persistence - H2, with Spring Security's own schema"
+  echo "schema-locations point at classpath:org/springframework/security/user-entities-schema.sql"
+  echo "and user-credentials-schema.sql, which live in spring-security-web, not in"
+  echo "spring-security-webauthn. Nothing creates these tables for you."
+  echo
+  ceremony register-and-login
+} 2>&1 | tee "$OUTPUT_DIR/pk-jdbc.txt"
+stop_app