Write an onboarding guide for this project

Create an onboarding guide for a developer new to this repository. Inspect its README, structure and configuration. Select the core feature emphasized in the README, otherwise a flow traceable from an entry point. Explain the selection without asking me to choose.

Trace input, processing, state or storage, and output through at most ten source files. Include a module diagram or text flow, real file references and starting points for three common changes.

List run and check commands only when defined in the project; do not execute them. Label inferred connections and unread areas. Deliver complete Markdown and verify its paths. The guide must explain responsibilities and behavior rather than merely reproduce the directory tree.

Execution contract:
Start directly. Do not ask me to approve a plan, choose files or fill in a template. Use only this project, this conversation and materials already provided; do not search unrelated projects or private history. Complete what the evidence supports and report missing inputs. If the task is inapplicable, explain why and stop without inventing a result.
Preserve existing files and uncommitted changes. Include complete proposed content in your reply; standalone artifacts may be saved under a new, unused filename. Do not install dependencies, change the environment, commit, push or deploy. Respect access and permission limits and report blocked work. Check your result once, deliver it and stop without asking whether to continue.