Simplify example app by removing Docker and web dashboard

[sueszli]

The example app had grown too complex with Docker orchestration, a full web dashboard UI and multi-stage builds. This made it harder for new users to understand the core Waymark functionality. By stripping it down to the essentials, the example now clearly demonstrates workflow patterns without infrastructure complexity.

Changes

• Removed: Multi-stage Docker builds, frontend dashboard, docker-compose orchestration
• Simplified: Makefile now runs Postgres in a container but tests run locally
• Flattened: Moved workflows.py directly to example_app/ root
• Testing: Direct workflow tests instead of HTTP integration tests

Impact

• Net deletion: ~3,450 lines removed, ~160 lines added
• Example app is now a minimal, focused demonstration of Waymark workflows
• Faster iteration and easier to understand for newcomers

[sueszli]

The behavior is the same and not impacted.

[piercefreeman]

@sueszli There's some value in the more complete example app, because it shows users how they'll actually integrate waymark with a serving pipeline. But agreed that the current scope is overkill. We can pair it down to a single workflow just to show the request/response/delegation logic within Docker.

Can you refactor what you have here into a new example-workflow folder (so we'll have example_app and example_workflows)... This example-workflows could also use a very basic README with run instructions.