feat: Add CI testing infrastructure with act_runner support

- Created scripts/test-ci-locally.sh to test Gitea Actions workflows locally using act_runner
- Created docker-compose.ci.yml for containerized CI test environment
- Updated .gitea/workflows/magnitude.yml to use docker-compose for CI
- Added scripts/README.md documenting the CI testing approach
- Created reusable test helpers in tests/playwright/

This allows developers to run the exact same workflow that CI runs, locally,
making it much easier to debug CI failures without push cycles.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

scripts/README.md

@@ -0,0 +1,65 @@
+# Development Scripts
+
+## test-ci-locally.sh
+
+Tests the Gitea Actions workflow locally using `act_runner` in Docker.
+
+### Purpose
+
+When CI tests fail, this script allows you to run the **exact same workflow** (`.gitea/workflows/magnitude.yml`) locally to debug issues without repeatedly pushing to trigger CI runs. It uses Gitea's official `act_runner` to execute the workflow in a containerized environment.
+
+### Usage
+
+```bash
+./scripts/test-ci-locally.sh
+```
+
+### What it does
+
+1. Loads environment variables from `.env` file
+2. Runs `gitea/act_runner:latest` Docker container with:
+   - Docker socket mounted (so act_runner can create containers)
+   - Current directory mounted as workspace
+   - Secrets passed from `.env` file
+3. Executes `.gitea/workflows/magnitude.yml` using act_runner's `exec` command
+4. The workflow then runs its steps:
+   - Checkout code
+   - Create .env file with secrets
+   - Run tests with docker-compose (starts SurrealDB, Next.js, Magnitude)
+   - Show logs on failure
+   - Upload test results
+   - Cleanup
+
+### Requirements
+
+- Docker installed and running
+- `.env` file with test credentials and secrets
+- Docker socket accessible at `/var/run/docker.sock`
+
+### How It Works
+
+The script uses Gitea's act_runner to execute the workflow YAML file. Act_runner creates containers according to the workflow definition, which in turn uses `docker-compose.ci.yml` to set up the test environment:
+
+```
+act_runner (Docker container)
+  ↓ executes .gitea/workflows/magnitude.yml
+  ↓ which runs docker-compose with:
+magnitude (Playwright container)
+  ↓ depends on (waits for health check)
+nextjs (Node.js container running pnpm dev)
+  ↓ depends on (waits for health check)
+surrealdb (SurrealDB container)
+```
+
+### Debugging CI Failures
+
+If Gitea Actions fail:
+
+1. Check the workflow logs for errors in Gitea UI
+2. Run `./scripts/test-ci-locally.sh` to execute the workflow locally
+3. The script will show the same steps and output as CI
+4. Fix issues based on the local test results
+5. Run script again to verify fix
+6. Commit and push once tests pass locally
+
+This is **much** faster than debugging via CI push cycles and gives you the exact same environment!