feat(typedef/crate-init): initialize alknet-typedef crate skeleton

Created crates/alknet-typedef/ with Cargo.toml depending on jsonschema 0.46
(default-features = false for WASM-cleanliness) and serde_json with
preserve_order. Added src/lib.rs with module declarations for all 9 modules
and skeleton source files for each. Added crate to workspace members list.

Verified: cargo check, clippy -D warnings, and build --workspace all succeed.
Dependency tree confirmed free of tokio/reqwest/rustls (WASM-clean).

tasks/typedef/crate-init.md

@@ -1,7 +1,7 @@
 ---
 id: typedef/crate-init
 name: Initialize alknet-typedef crate with Cargo.toml, dependencies, and module skeleton
-status: pending
+status: completed
 depends_on: []
 scope: moderate
 risk: low
@@ -128,4 +128,15 @@ Each module file gets a doc comment and `// TODO: implement` marker.
 
 ## Summary
 
-> To be filled on completion
+Initialized the `alknet-typedef` crate skeleton. Created `crates/alknet-typedef/`
+with `Cargo.toml` (depending on `jsonschema = "0.46"` with `default-features = false`
+for WASM-cleanliness, and `serde_json` with `preserve_order`), `src/lib.rs` with
+module declarations for all 9 modules, and 9 skeleton source files (`error.rs`,
+`schema.rs`, `data_access.rs`, `offset_map.rs`, `layout_builder.rs`,
+`sequential_reader.rs`, `tunion.rs`, `validation.rs`, `engine.rs`) each with a
+doc comment and `// TODO: implement` marker. Added the crate to the workspace
+`members` list in the root `Cargo.toml`. Verified: `cargo check -p alknet-typedef`,
+`cargo clippy -p alknet-typedef -- -D warnings`, and `cargo build --workspace` all
+succeed. Confirmed no tokio/reqwest/rustls in the dependency tree (WASM-clean by
+construction). Used the published `jsonschema` crate from crates.io (v0.46.10)
+rather than the workspace reference copy at `/workspace/jsonschema/`.