feat: run tests in background with progress polling

Improve the testing dashboard to run pytest in the background:

- Add background task execution using FastAPI's BackgroundTasks
- Create test_runner_tasks.py following existing background task pattern
- API now returns immediately after starting the test run
- Frontend polls for status every 2 seconds until completion
- Show running indicator with elapsed time counter
- Resume polling if user navigates away and returns while tests running
- Tests continue running even if user closes the page

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

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

app/services/test_runner_service.py

@@ -25,6 +25,25 @@ class TestRunnerService:
     def __init__(self):
         self.project_root = Path(__file__).parent.parent.parent
 
+    def create_test_run(
+        self,
+        db: Session,
+        test_path: str = "tests",
+        triggered_by: str = "manual",
+    ) -> TestRun:
+        """Create a test run record without executing tests"""
+        test_run = TestRun(
+            timestamp=datetime.now(UTC),
+            triggered_by=triggered_by,
+            test_path=test_path,
+            status="running",
+            git_commit_hash=self._get_git_commit(),
+            git_branch=self._get_git_branch(),
+        )
+        db.add(test_run)
+        db.flush()
+        return test_run
+
     def run_tests(
         self,
         db: Session,
@@ -33,7 +52,7 @@ class TestRunnerService:
         extra_args: list[str] | None = None,
     ) -> TestRun:
         """
-        Run pytest and store results in database
+        Run pytest synchronously and store results in database
 
         Args:
             db: Database session
@@ -44,21 +63,19 @@ class TestRunnerService:
         Returns:
             TestRun object with results
         """
-        # Create test run record
-        test_run = TestRun(
-            timestamp=datetime.now(UTC),
-            triggered_by=triggered_by,
-            test_path=test_path,
-            status="running",
-        )
-        db.add(test_run)
-        db.flush()  # Get the ID
+        test_run = self.create_test_run(db, test_path, triggered_by)
+        self._execute_tests(db, test_run, test_path, extra_args)
+        return test_run
 
+    def _execute_tests(
+        self,
+        db: Session,
+        test_run: TestRun,
+        test_path: str,
+        extra_args: list[str] | None,
+    ) -> None:
+        """Execute pytest and update the test run record"""
         try:
-            # Get git info
-            test_run.git_commit_hash = self._get_git_commit()
-            test_run.git_branch = self._get_git_branch()
-
             # Build pytest command with JSON output
             with tempfile.NamedTemporaryFile(mode='w', suffix='.json', delete=False) as f:
                 json_report_path = f.name
@@ -66,7 +83,7 @@ class TestRunnerService:
             pytest_args = [
                 "python", "-m", "pytest",
                 test_path,
-                f"--json-report",
+                "--json-report",
                 f"--json-report-file={json_report_path}",
                 "-v",
                 "--tb=short",
@@ -120,8 +137,6 @@ class TestRunnerService:
             test_run.status = "error"
             logger.error(f"Error running tests: {e}")
 
-        return test_run
-
     def _process_json_report(self, db: Session, test_run: TestRun, report: dict):
         """Process pytest-json-report output"""
         summary = report.get("summary", {})