Add a first-class Component entity to Sztab so that issues can be categorized, routed, and owned by the subsystem they belong to. Components are a foundational issue management primitive — without them, all issues land in an undifferentiated pool that doesn't scale beyond a small team.

A real example for a project like Sztab itself:

When an issue is filed against Database, Joan is notified. The reporter doesn't need to know the team structure — they pick the closest component and the system routes it correctly.

Acceptance Criteria

• Component entity: id, name, description, project FK, defaultAssignee FK (optional)
• Project gains a components collection
• REST: GET/POST/DELETE /api/projects/{id}/components
• Issue.component changes from plain String to Component FK
• Create modal: component dropdown shown only when project has components configured; hidden otherwise
• Edit modal: same conditional rendering
• Project settings: new Components tab to add/rename/delete components and assign default owners
• DEFAULT_COMPONENT sentinel removed from codebase
• Flyway migration included

Comments

1. We'll use Project-scoped components?
2. Will auto-assign to component owner on creation
3. If a project has components configured, then each issue in the project must be in one of the defined components.