feat: add pytest testing dashboard with run history and statistics

Add a new Testing Dashboard page that replaces the old Testing Hub with
pytest integration:

- Database models for test runs, results, and collections (TestRun,
  TestResult, TestCollection)
- Test runner service that executes pytest with JSON reporting and
  stores results in the database
- REST API endpoints for running tests, viewing history, and statistics
- Dashboard UI showing pass rates, trends, tests by category, and top
  failing tests
- Alembic migration for the new test_* tables

The dashboard allows admins to:
- Run pytest directly from the UI
- View test run history with pass/fail statistics
- See trend data across recent runs
- Identify frequently failing tests
- Collect test information without running

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

app/routes/admin_pages.py

@@ -789,14 +789,33 @@ async def admin_icons_page(
 
 
 @router.get("/testing", response_class=HTMLResponse, include_in_schema=False)
+async def admin_testing_dashboard(
+    request: Request,
+    current_user: User = Depends(get_current_admin_from_cookie_or_header),
+    db: Session = Depends(get_db),
+):
+    """
+    Render testing dashboard page.
+    pytest results and test coverage overview.
+    """
+    return templates.TemplateResponse(
+        "admin/testing-dashboard.html",
+        {
+            "request": request,
+            "user": current_user,
+        },
+    )
+
+
+@router.get("/testing-hub", response_class=HTMLResponse, include_in_schema=False)
 async def admin_testing_hub(
     request: Request,
     current_user: User = Depends(get_current_admin_from_cookie_or_header),
     db: Session = Depends(get_db),
 ):
     """
-    Render testing hub page.
-    Central hub for all test suites and QA tools.
+    Render manual testing hub page.
+    Central hub for all manual test suites and QA tools.
     """
     return templates.TemplateResponse(
         "admin/testing-hub.html",