CI: build + CodeQL required checks fail independent of PR content #30

PR #28 merged green on its own checks (fmt, wasm-test, Analyze rust/actions) but two required checks fail for reasons unrelated to any PR, so every PR is BLOCKED and needs an admin override.

1. build (cargo clippy --workspace --all-targets -- -D warnings): toolchain drift. CI pins dtolnay/rust-toolchain@stable, which installs the latest stable at run time. Current stable clippy raises double_must_use inside async_trait-generated code at crates/stitch/src/backend/mod.rs:29-30 (the Db trait). The repo rule forbids #[allow(...)], so the real fix is bumping async-trait to a macro version that does not emit the redundant must_use, or pinning the CI toolchain to a known-good version. main's last CI run predates the lint and would fail today if re-run.

2. CodeQL required check fails in ~2s while the actual Analyze (rust) and Analyze (actions) jobs pass. Looks like a gate/default-setup artifact, not a code finding. Reconcile the required-check contexts with the jobs that actually run.

Both are repo CI-health issues, not defects in feature changes.