feat: add analysis model objects

phases/analysis-model-objects/step6.md

@@ -0,0 +1,55 @@
+# Step 6: load-base-interface
+
+## Read First
+
+Read these files before editing:
+
+- `/AGENTS.md`
+- `/docs/AGENT_RULES.md`
+- `/docs/ARCHITECTURE.md`
+- `/docs/implementation-plans/analysis-model-objects-implementation-plan.md`
+- `/include/fesa/core/LoadDefinition.hpp`
+
+## Task
+
+Add load model base and nodal load object.
+
+Allowed files:
+
+- Create `/include/fesa/load/Load.hpp`
+- Create `/include/fesa/load/NodalLoad.hpp`
+- Create `/src/load/NodalLoad.cpp`
+- Create `/tests/load/load_base_test.cpp`
+- Modify `/CMakeLists.txt`
+
+Required behavior:
+
+- `Load` has virtual destructor and a load kind enum.
+- `NodalLoad` derives from `Load`.
+- Stores node id, DOF, and value.
+- No global vector assembly in this phase.
+
+## Tests To Write First
+
+Write `/tests/load/load_base_test.cpp` before production changes:
+
+- Access `NodalLoad` through `const Load&`.
+- Verify kind, node id, DOF, value.
+- Verify deletion through `std::unique_ptr<Load>`.
+
+Run targeted build and confirm RED.
+
+## Acceptance Criteria
+
+Run:
+
+```powershell
+python scripts/validate_workspace.py
+ctest --test-dir build/msvc-debug --output-on-failure -C Debug -R model-object
+```
+
+Update step 6 status.
+
+## Do Not
+
+- Do not assemble forces or apply time/load factors.