Set up GameCI pipeline

**What**

Add automated testing for the Unity package and configure CI using GameCI to run test validation on pull requests and main branch updates.

**Why**

Reliable CI feedback is required to prevent regressions and ensure package quality as OCR SDK features evolve.

**How**

* Configure GameCI workflow to run tests in GitHub Actions
* Run pipeline on pull requests and pushes to `main`
* Publish test results/artifacts for easier debugging
* Document local test run and CI behavior

**Acceptance Criteria**

* Unity tests exist for core package behavior and are runnable in CI
* GameCI workflow runs automatically on PRs and pushes to `main`
* CI reports pass/fail status with actionable output
* Documentation explains how tests are run locally and in CI

**Estimation**

**Dependencies**

Start by locating the Unity package's existing tests and any current GitHub Actions workflows. Configure GameCI to run Unity tests on pull requests and pushes to main, publish actionable results or artifacts, and document local and CI test behavior. Done means core package tests run successfully in CI with pass/fail status and the requested documentation is present.

Written by the indexing model from the issue text.