feat: add analysis model objects

phases/analysis-model-objects/step0.md

@@ -0,0 +1,54 @@
+# Step 0: model-object-contract
+
+## Read First
+
+Read these files before editing:
+
+- `/AGENTS.md`
+- `/docs/PLAN.md`
+- `/docs/PROGRESS.md`
+- `/docs/WORKNOTE.md`
+- `/docs/AGENT_RULES.md`
+- `/docs/PRD.md`
+- `/docs/ADR.md`
+- `/docs/ARCHITECTURE.md`
+- `/docs/implementation-plans/domain-model-foundation-implementation-plan.md`
+- `/include/fesa/core/Domain.hpp`
+
+## Task
+
+Create `/docs/implementation-plans/analysis-model-objects-implementation-plan.md`.
+
+The document must define the model object layer that will be stored by `Domain`:
+
+- `Node` model object.
+- abstract `Element` base and MITC4 model object skeleton.
+- abstract `Material` base and linear elastic material model object.
+- shell property/section model object.
+- abstract `Load` base and nodal load model object.
+- abstract `BoundaryCondition` base and single-point constraint model object.
+- `Domain` RAII ownership of polymorphic model objects through `std::unique_ptr`.
+
+State explicitly that this phase does not implement MITC4 stiffness, material constitutive matrices, global force assembly, boundary-condition matrix application, equation numbering, solver vectors, HDF5 output, reference comparison, or reference-solver execution.
+
+Document how existing `*Definition` value objects remain compatible as input DTOs until parser/factory work replaces or maps them.
+
+## Tests To Write First
+
+This is a documentation planning step. Do not write C++ production code in this step.
+
+## Acceptance Criteria
+
+Run:
+
+```powershell
+python -m unittest discover -s scripts -p "test_*.py"
+python scripts/validate_workspace.py
+```
+
+Update `/phases/analysis-model-objects/index.json` step 0 with `completed`, `error`, or `blocked`.
+
+## Do Not
+
+- Do not change C++ code in this step.
+- Do not change MITC4 formulation, I/O contracts, reference artifacts, or tolerance policy.