feat: start abaqus input parser

phases/abaqus-input-parser/step2.md

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+# Step 2: syntax-diagnostics
+
+## 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/io/abaqus/input_parser.hpp`
+- `/src/fesa/io/abaqus/input_parser.cpp`
+- `/tests/unit/abaqus_input_parser_mesh_test.cpp`
+
+Review completed step summaries in `/phases/abaqus-input-parser/index.json`.
+
+## Task
+
+Add structured diagnostics for parser syntax and unsupported subset behavior.
+
+Required behavior:
+
+- Unsupported keywords produce `Status::is_ok() == false` with an error
+  diagnostic code and message that identifies the keyword.
+- Malformed `*NODE` and `*ELEMENT` data lines produce error diagnostics.
+- Missing required `TYPE` on `*ELEMENT` produces an error diagnostic.
+- Unsupported element types produce an error diagnostic and do not add that
+  element.
+- Diagnostics must include enough context in the message to locate the line
+  number.
+- Existing valid mesh parser behavior remains unchanged.
+
+## Tests To Write First
+
+Extend `/tests/unit/abaqus_input_parser_mesh_test.cpp` or add
+`/tests/unit/abaqus_input_parser_diagnostics_test.cpp` before production code.
+
+Test:
+
+- unsupported keyword failure;
+- malformed node row failure;
+- missing element `TYPE` failure;
+- unsupported element type failure.
+
+Run the targeted CTest and confirm the new tests fail for missing behavior
+before implementation.
+
+## Acceptance Criteria
+
+```powershell
+ctest --test-dir build/msvc-debug --output-on-failure -C Debug -R abaqus_input_parser
+python -m unittest discover -s scripts -p "test_*.py"
+python scripts/validate_workspace.py
+```
+
+## Verification Procedure
+
+Update step 2 status with summary or a concrete error/blocked reason.
+
+## Forbidden
+
+- Do not add new semantic model fields except what diagnostics require.
+- Do not add material, section, step, boundary, or load parsing.