ci: name IR-level round-trip corpus step explicitly (refs #130 — surface .twasm corpus blocked on #127) (#157)

## Summary

`crates/typed-wasm-codegen/tests/corpus.rs` is a 223-LoC IR-level
property test: 512 deterministically-generated IR modules, each asserts
`verify_from_module(emit(m)) == OK`. It is green today and runs as part
of `cargo test --workspace --locked` in `e2e.yml`'s `cargo-verify` job —
but is not named, so any regression in the `verify(emit(m))` loop
surfaces as an opaque workspace-test failure.

This PR adds an explicit, named step that re-runs the corpus alone right
after the workspace test. The double-run cost is ~0.06s (the binary is
already built) and the value is "regression has a clearly-named CI
failure."

## Out of scope

Surface `.twasm` → wasm round-trip is **blocked on #127** (front-end →
IR seam). This is the cheap-wire half of #130 only. Tracking the
surface-corpus half as ongoing work under #130.

## Test plan

- [x] `cargo test --test corpus -p typed-wasm-codegen --locked` — 3
tests pass (`generated_corpus_round_trips`, `wired_examples_round_trip`,
`malformed_modules_are_rejected`)
- [x] YAML lints clean (9-line diff to `e2e.yml`)

Refs #130, refs #127.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: hyperpolymath

.github/workflows/e2e.yml

@@ -214,3 +214,12 @@ jobs:
 
       - name: Cargo test (workspace)
         run: cargo test --workspace --locked
+
+      # Explicit named step for the IR-level round-trip corpus (#130).
+      # Already covered by the workspace test above, but naming it
+      # explicitly makes any regression in the verify(emit(m)) loop
+      # surface as a clearly-named failure. Surface .twasm corpus is
+      # blocked on the front-end → IR seam (#127); this is the cheap-wire
+      # half of #130.
+      - name: Round-trip soundness corpus (IR-level slice — refs #130)
+        run: cargo test --test corpus -p typed-wasm-codegen --locked