Abaqus input writer and deck.write (M3) (#22)

* decks: Abaqus input writer with golden decks, read-back, Jacobian and unsupported tests

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01NmAttHhUZTokgPeEJia8sm

* engine: deck.write command (format dispatch, atomic file write), docs

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01NmAttHhUZTokgPeEJia8sm

* decks: format table, one resolve per write, direct buffer writes; engine: shared path parameter

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01NmAttHhUZTokgPeEJia8sm

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Co-authored-by: jyviko <2501648+jyviko@users.noreply.github.com>
Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>

docs/architecture.md

@@ -22,7 +22,7 @@ crates in strictly lower layers.
 | L1 | `modelcraft-geometry` | The only door to SolidCraft: opens `.solidcraft` designs (rebuilt from their timeline, bodies with persistent face names), B-rep bodies, measures, tessellation into a face-tagged `SurfaceMesh`; face-tagged 3MF files read into the same type without the kernel (docs/formats/tagged-mesh.md). No SolidCraft type in its API. | started |
 | L1 | `modelcraft-mesh` | Surface preparation (weld, watertightness, feature edges), robust predicates, Delaunay tetrahedralization and refinement, Voronoi-based optimization, hex meshing, quality metrics. | started |
 | L1 | `modelcraft-solver` | Element formulations, assembly, sparse linear static and modal solution. | planned |
-| L1 | `modelcraft-decks` | Abaqus input, Nastran bulk data and LS-DYNA keyword readers and writers, to and from `model`. | planned |
+| L1 | `modelcraft-decks` | Abaqus input, Nastran bulk data and LS-DYNA keyword readers and writers, to and from `model`. Text out, no file system; `deck.write` saves it. | started |
 | L1 | `modelcraft-render` | Display data without a GPU dependency: the visible faces, element edges and nodes of a model, the orbit camera, a CPU rasterizer for headless snapshots; contour maps later. | started |
 | L2 | `modelcraft-doc` | The document: geometry, mesh, model, results, history. | planned |
 | L3 | `modelcraft-io` | `.modelcraft` files (docs/formats/modelcraft.md): text model definition, binary mesh, geometry references with content hashes, the journal; atomic saves; autosave storage for crash recovery. Bytes in, bytes out; the file system only in `fs` and `recovery`. Result files later. | started |