refactor!: rename slhx to hemx

Rename the tracked product identity, crate/package names, Rust paths/macros, generated artifacts, runtime files, public attributes, examples, docs, requirements, and tests from slhx to hemx without compatibility shims.

Verified with cargo run -p hemx-xtask -- test, cargo test -p hemx-derive --test compile_fail, cargo test -p hemx-js, cargo test -p hemx-axum, cargo test -p hemx-v0-examples, cargo check --workspace, redgate list, redgate refs, redgate health --strict, git diff --check, and git grep/ls-files legacy-name audits.

req: misc/001

req: codegen/001

req: component/004

req: runtime/001

hemx-derive/build.rs

@@ -0,0 +1,4 @@
+fn main() {
+    let out = std::path::PathBuf::from(std::env::var_os("OUT_DIR").unwrap());
+    std::fs::write(out.join("hemx.generated.rs"), "").unwrap();
+}