Define product outcomes and success measures

Define the outcomes Feedbacker must produce for educators, assessment teams, institutions, and affected students.

### Deliverables
- A concise outcome statement for each primary stakeholder group
- Measurable success indicators for consistency, traceability, educator control, usability, and scale
- Explicit non-goals and failure conditions

### Done when
The measures are testable and align with docs/PROJECT.md.

Start by reading docs/PROJECT.md to understand the existing project direction and terminology. Define concise outcomes for educators, assessment teams, institutions, and affected students, then add testable indicators for consistency, traceability, educator control, usability, and scale. Done means the document includes explicit non-goals and failure conditions and its measures align with docs/PROJECT.md.

Written by the indexing model from the issue text.