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/unit/test_intent.py

@@ -16,8 +16,10 @@ from app.intent import (
 from app.registry import AgentConfig
 
 
-def _make_agent(name: str, desc: str = "test", permission: str = "read") -> AgentConfig:
-    return AgentConfig(name=name, description=desc, permission=permission, tools=["fallback_respond"])
+def _make_agent(name: str, desc: str = "test", perm: str = "read") -> AgentConfig:
+    return AgentConfig(
+        name=name, description=desc, permission=perm, tools=["fallback_respond"],
+    )
 
 
 @pytest.mark.unit