fix: resolve ruff lint errors in Phase 2 code

- Move intent imports to TYPE_CHECKING block in graph.py (TC001)
- Rename test classes to CapWords convention (N801)
- Fix line length violations across test files (E501)
- Auto-fix import sorting (I001)

backend/tests/integration/test_phase2_checkpoints.py

@@ -90,7 +90,7 @@ def _agent(name: str, desc: str, perm: str = "read") -> AgentConfig:
 # ---------------------------------------------------------------------------
 
 @pytest.mark.integration
-class TestCheckpoint1_OrderQueryRouting:
+class TestCheckpoint1OrderQueryRouting:
     """Verify intent classifier routes order queries to order_lookup."""
 
     @pytest.mark.asyncio
@@ -161,7 +161,7 @@ class TestCheckpoint1_OrderQueryRouting:
 # ---------------------------------------------------------------------------
 
 @pytest.mark.integration
-class TestCheckpoint2_MultiIntentSequential:
+class TestCheckpoint2MultiIntentSequential:
     """Verify multi-intent classified and hint injected for sequential execution."""
 
     @pytest.mark.asyncio
@@ -235,7 +235,7 @@ class TestCheckpoint2_MultiIntentSequential:
 # ---------------------------------------------------------------------------
 
 @pytest.mark.integration
-class TestCheckpoint3_AmbiguousClarification:
+class TestCheckpoint3AmbiguousClarification:
     """Verify ambiguous messages trigger clarification prompt."""
 
     @pytest.mark.asyncio
@@ -263,7 +263,9 @@ class TestCheckpoint3_AmbiguousClarification:
         mock_classifier.classify = AsyncMock(return_value=ClassificationResult(
             intents=(),
             is_ambiguous=True,
-            clarification_question="Could you please provide more details about what you need help with?",
+            clarification_question=(
+                "Could you please provide more details about what you need help with?"
+            ),
         ))
         graph.intent_classifier = mock_classifier
         mock_registry = MagicMock()
@@ -294,7 +296,7 @@ class TestCheckpoint3_AmbiguousClarification:
 # ---------------------------------------------------------------------------
 
 @pytest.mark.integration
-class TestCheckpoint4_InterruptTTLAutoCancel:
+class TestCheckpoint4InterruptTTLAutoCancel:
     """Verify interrupt TTL expiration triggers auto-cancel and retry prompt."""
 
     @pytest.mark.asyncio
@@ -361,7 +363,7 @@ class TestCheckpoint4_InterruptTTLAutoCancel:
 # ---------------------------------------------------------------------------
 
 @pytest.mark.integration
-class TestCheckpoint5_WebhookEscalation:
+class TestCheckpoint5WebhookEscalation:
     """Verify webhook escalation sends POST and retries on failure."""
 
     @pytest.mark.asyncio
@@ -442,7 +444,7 @@ class TestCheckpoint5_WebhookEscalation:
 # ---------------------------------------------------------------------------
 
 @pytest.mark.integration
-class TestCheckpoint6_EcommerceTemplate:
+class TestCheckpoint6EcommerceTemplate:
     """Verify e-commerce template loads with correct agents."""
 
     def test_ecommerce_template_loads_4_agents(self) -> None: