Split web/ into senbei-wasm crate + static assets

The Rust bindings move from web/src to a top-level senbei-wasm crate (still
outside the workspace, own Cargo.lock), matching the other senbei-* crates.
web/ keeps only the static frontend; wasm-pack emits the JS/wasm package into
web/pkg/ via --out-dir. JS glue renamed senbei_web -> senbei_wasm with the
crate.

Cargo.toml

@@ -7,9 +7,9 @@ members = [
     "senbei-pe",
 ]
 default-members = ["senbei-cli"]
-# The wasm frontend is its own crate (own Cargo.lock, cdylib) and stays outside
-# the workspace.
-exclude = ["web"]
+# The wasm bindings crate is its own crate (own Cargo.lock, cdylib) and stays
+# outside the workspace.
+exclude = ["senbei-wasm"]
 resolver = "2"
 
 [workspace.package]