refactor(core): introduce Unit of Work and remove commits from services

- Add UnitOfWork context manager in domain/unit_of_work.py with commit/rollback/flush API and auto-rollback on exception

- Remove all db.commit() from test_workflow_service (8 calls), notification_service (4 calls), status_service (1 call)

- Services now only stage changes via db.add/db.flush; caller owns the transaction boundary

- Update routers/tests.py: wrap 9 workflow endpoints in UnitOfWork context managers

- Update routers/notifications.py: wrap mark_as_read and mark_all_as_read in UnitOfWork

backend/app/services/test_workflow_service.py

@@ -7,8 +7,9 @@ for each step in the test lifecycle:
                                                                   ↓
                                                            rejected → draft
 
-Every public function validates the transition, mutates the test, writes an
-audit-log entry, and commits the session.
+Every public function validates the transition, mutates the test, and writes
+an audit-log entry.  The caller (router) is responsible for committing the
+session via the Unit of Work pattern.
 """
 
 import logging
@@ -122,7 +123,6 @@ def start_execution(db: Session, test: Test, user: User) -> Test:
     )
     test.execution_date = now
     test.red_started_at = now
-    db.commit()
     return test
 
 
@@ -161,7 +161,6 @@ def submit_red_evidence(db: Session, test: Test, user: User) -> Test:
     # Start Blue Team timer
     test.blue_started_at = now
     test.blue_paused_seconds = 0
-    db.commit()
     return test
 
 
@@ -196,7 +195,6 @@ def submit_blue_evidence(db: Session, test: Test, user: User) -> Test:
         description=f"Blue Team evaluation: {test.name}",
     )
 
-    db.commit()
     return test
 
 
@@ -222,7 +220,6 @@ def pause_timer(db: Session, test: Test, user: User) -> Test:
         entity_id=test.id,
         details={"state": test.state.value},
     )
-    db.commit()
     return test
 
 
@@ -252,7 +249,6 @@ def resume_timer(db: Session, test: Test, user: User) -> Test:
         entity_id=test.id,
         details={"paused_seconds": paused_seconds, "state": test.state.value},
     )
-    db.commit()
     return test
 
 
@@ -421,14 +417,12 @@ def check_dual_validation(db: Session, test: Test) -> Test:
 
     if red_status == "rejected" or blue_status == "rejected":
         test.state = TestState.rejected
-        db.commit()
         try:
             notify_test_state_change(db, test, "rejected")
         except Exception as e:
             logger.warning("Notification failed for test %s (rejected): %s", test.id, e, exc_info=True)
     elif red_status == "approved" and blue_status == "approved":
         test.state = TestState.validated
-        db.commit()
         # Invalidate cached scores — a validation changes org-level numbers
         try:
             from app.services.score_cache import invalidate
@@ -439,10 +433,6 @@ def check_dual_validation(db: Session, test: Test) -> Test:
             notify_test_state_change(db, test, "validated")
         except Exception as e:
             logger.warning("Notification failed for test %s (validated): %s", test.id, e, exc_info=True)
-    else:
-        # One side hasn't voted yet — stay in_review, just flush
-        db.commit()
-
     return test
 
 
@@ -533,8 +523,7 @@ def handle_remediation_completed(db: Session, test: Test, user: User) -> Test |
             entity_id=retest.id,
         )
 
-    db.commit()
-    db.refresh(retest)
+    db.flush()
     return retest
 
 
@@ -599,5 +588,4 @@ def reopen_test(db: Session, test: Test, user: User) -> Test:
     test.red_paused_seconds = 0
     test.blue_paused_seconds = 0
 
-    db.commit()
     return test