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/app/graph.py

@@ -9,13 +9,13 @@ from langgraph.prebuilt import create_react_agent
 from langgraph_supervisor import create_supervisor
 
 from app.agents import get_tools_by_names
-from app.intent import ClassificationResult, IntentClassifier
 
 if TYPE_CHECKING:
     from langchain_core.language_models import BaseChatModel
     from langgraph.checkpoint.postgres.aio import AsyncPostgresSaver
     from langgraph.graph.state import CompiledStateGraph
 
+    from app.intent import ClassificationResult, IntentClassifier
     from app.registry import AgentRegistry
 
 logger = logging.getLogger(__name__)