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

examples/techdemo/templates/partials/issue_lane.heml

@@ -1,4 +1,4 @@
-<section +class="self.class" +data-lane="self.lane_id" data-slhx-handle="move_to_lane" data-slhx-on="drop">
+<section +class="self.class" +data-lane="self.lane_id" data-hemx-handle="move_to_lane" data-hemx-on="drop">
   <h3>{+ self.title +}</h3>
   <p>{+ self.description +}</p>
   <template h-for="card in &self.cards">