feat: start abaqus input parser

phases/abaqus-input-parser/step3.md

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+# Step 3: sets-and-section-properties
+
+## Read First
+
+Read these files before editing:
+
+- `/AGENTS.md`
+- `/docs/ARCHITECTURE.md`
+- `/docs/ADR.md`
+- `/docs/io-definitions/abaqus-input-parser-io.md`
+- `/src/fesa/model/domain.hpp`
+- `/src/fesa/model/element.hpp`
+- `/src/fesa/model/property.hpp`
+- `/src/fesa/io/abaqus/input_parser.hpp`
+- `/src/fesa/io/abaqus/input_parser.cpp`
+
+Review completed parser tests and phase summaries first.
+
+## Task
+
+Extend the model and parser only as needed to represent set membership and
+section-to-property assignment for V0 bar/truss models.
+
+Required behavior:
+
+- Parse `*NSET, NSET=<name>` node membership rows.
+- Parse `*ELSET, ELSET=<name>` element membership rows.
+- Parse one V0 section keyword that assigns a material name to an element set.
+  Prefer the smallest section subset compatible with the current V0 element
+  path.
+- Preserve deterministic member ordering as read, unless the I/O contract
+  explicitly states otherwise.
+- Keep `Domain` as the owner of model definition data. Do not store equation ids
+  on nodes or elements.
+
+## Tests To Write First
+
+Add focused C++ tests before production code:
+
+- a model test for any new set/section semantic model API;
+- a parser test proving `*NSET`, `*ELSET`, and the selected section keyword map
+  into the semantic model.
+
+Run targeted CTest and confirm the tests fail before implementation.
+
+## Acceptance Criteria
+
+```powershell
+ctest --test-dir build/msvc-debug --output-on-failure -C Debug -R "(model_|abaqus_input_parser_)"
+python -m unittest discover -s scripts -p "test_*.py"
+python scripts/validate_workspace.py
+```
+
+## Verification Procedure
+
+Update step 3 status with summary or a concrete error/blocked reason.
+
+## Forbidden
+
+- Do not parse materials beyond names needed for section linkage.
+- Do not add loads, boundary conditions, or analysis steps.
+- Do not generate or modify reference artifacts.