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

---------

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

crates/engine/src/cmd/mod.rs

@@ -1,5 +1,6 @@
 //! The command registry. Each area has its own module; [`ALL`] lists every command.
 
+pub(crate) mod deck;
 pub(crate) mod define;
 mod edit;
 pub(crate) mod file;
@@ -66,6 +67,7 @@ pub static ALL: &[CommandSpec] = &[
     file::RECOVERY_DISCARD,
     edit::UNDO,
     edit::REDO,
+    deck::WRITE,
 ];
 
 /// A required label parameter (1..=u32::MAX; the model checks its own range).