feat: add testing framework and initial test cases

- Updated package.json to include Vitest and testing dependencies.
- Created test cases for SuitePicker component to validate selection logic.
- Added tests for ReportsPage to ensure correct report grouping and ordering.
- Implemented read-only enforcement tests for SuitePage to prevent actions on built-in suites.
- Introduced a setup file for Vitest to include jest-dom matchers and cleanup after tests.
- Modified ReportsPage to group reports by model and display them accordingly.
- Enhanced API types to include suite_scope and question_count for better report handling.

server/schemas.py

@@ -169,6 +169,11 @@ class ReportSummary(BaseModel):
     model_label: str
     size_bytes: int
     modified_at: float
+    #: Parsed out of the filename so the list can group by model and show what
+    #: each run actually covered. Older reports predate the scheme and leave
+    #: these empty rather than guessing.
+    suite_scope: str = ""
+    question_count: Optional[int] = None
 
 
 class ReportDetail(ReportSummary):