feat: add analysis model objects

phases/analysis-model-objects/step1.md

@@ -0,0 +1,53 @@
+# Step 1: node-model-class
+
+## 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/Node.hpp`
+- `/tests/core/node_test.cpp`
+
+## Task
+
+Refine the existing `Node` model class contract without adding solver state.
+
+Allowed files:
+
+- Modify `/include/fesa/core/Node.hpp`
+- Modify `/src/core/Domain.cpp` only if constructor/accessor definitions move or change
+- Modify `/tests/core/node_test.cpp`
+
+Required behavior:
+
+- `Node` exposes `id()`, `coordinates()`, `x()`, `y()`, `z()`.
+- `Node` exposes `static constexpr std::size_t dofCount()` or equivalent compile-time DOF count of 6.
+- `Node` does not store equation ids, displacements, residuals, reactions, or constraints.
+
+## Tests To Write First
+
+Extend `/tests/core/node_test.cpp` before production changes:
+
+- Verify `Node::dofCount() == 6`.
+- Verify coordinate order is preserved.
+- Verify the returned coordinate data is const from a const `Node`.
+
+Run the targeted build and confirm RED before implementation.
+
+## Acceptance Criteria
+
+Run:
+
+```powershell
+python scripts/validate_workspace.py
+ctest --test-dir build/msvc-debug --output-on-failure -C Debug -R domain
+```
+
+Update `/phases/analysis-model-objects/index.json` step 1 with status and summary.
+
+## Do Not
+
+- Do not add equation ids or solver state to `Node`.