feat: initial approval workflow engine with in-memory and JDBC storage

Lightweight linear approval engine (v0.1):

- ordo-api: domain model, OrdoEngine port, repository SPI with
  conditional updates (insertIfAbsent, completeIfPending) and a
  TransactionExecutor port for atomic multi-step writes
- ordo-core: DefaultOrdoEngine running register/start/approve/reject
  inside a transaction boundary; in-memory engine and repositories
- ordo-storage-jdbc: thread-bound JDBC transactions, normalized V1
  schema migration, Jackson-based ProcessContext JSON codec
- tests: unit tests plus H2 integration tests; PostgreSQL integration
  tests run against a local instance via ordo.test.pg.* properties and
  skip when unreachable

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

.idea/misc.xml

@@ -0,0 +1,14 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project version="4">
+  <component name="ExternalStorageConfigurationManager" enabled="true" />
+  <component name="MavenProjectsManager">
+    <option name="originalFiles">
+      <list>
+        <option value="$PROJECT_DIR$/pom.xml" />
+      </list>
+    </option>
+  </component>
+  <component name="ProjectRootManager" version="2" languageLevel="JDK_21" default="true" project-jdk-name="dragonwell-21" project-jdk-type="JavaSDK">
+    <output url="file://$PROJECT_DIR$/out" />
+  </component>
+</project>