Set up initial stock entities and API surface

[JacobChwastek]

Goal

Set up the first usable slice of the WiSave Stock service: core stock domain entities, API endpoints, and the foundation needed for portfolio/watchlist flows.

Scope

• Define the initial stock domain entities and relationships.
• Add the first API endpoints needed by the UI and Portal.
• Establish request/response contracts for stock, portfolio, watchlist, and related lookup flows where applicable.
• Keep the service structure ready for future stock features such as overview, opportunities, research, and reports.
• Add validation, auth expectations, and error handling consistent with the rest of WiSave services.

Acceptance criteria

• Initial stock entities are modeled and persisted where needed.
• API endpoints expose the first stock data flows needed by consumers.
• Contracts are documented enough for Portal/UI integration.
• Basic tests or verification notes cover the first entity/API behavior.

Notes

This tracks the setup work already in progress: adding the first entities, API surface, and service foundation.