Add Maven Wrapper and standardize Maven invocation across CI/docs

[Copilot]

This PR adds Maven Wrapper support to integrations-api, aligned with the approach used in cryptofs, so builds no longer depend on a preinstalled system Maven. CI workflows and project docs are updated to use the wrapper consistently.

• Wrapper bootstrap

  • Added mvnw, mvnw.cmd, and .mvn/wrapper/maven-wrapper.properties.
  • Pinned wrapper config to Maven 3.9.16 with SHA-256 verification.

• CI command standardization

  • Replaced mvn with ./mvnw in:
    • .github/workflows/build.yml
    • .github/workflows/codeql-analysis.yml
  • Includes version-setting, project-version evaluation, compile/verify, and deploy invocations.

• Developer-facing build docs

  • Updated README.md build section to use wrapper-based invocation and list JDK requirement.

Example command transition:

# before
mvn -B verify --no-transfer-progress

# after
./mvnw -B verify --no-transfer-progress