fix(ci): drop the beta-Rust CodeQL leg (was cancelled/hanging), keep actions

The CodeQL matrix analysed `actions` + `rust`. CodeQL's Rust support is beta:
that leg cancels/hangs and never resolves (the recurring "CodeQL checks 2
things forever" symptom), providing zero real coverage. Removing it leaves the
`actions` leg (this repo's primary analysable surface, per the workflow's own
comment), so the matrix stays non-empty (no zero-jobs startup_failure).

Rust security should be covered natively instead: rust.yml already runs
clippy + build + test. A cargo-audit gate is a recommended follow-up — verified
locally that `cargo audit` runs and already flags a real vuln in shared-context
(crossbeam-epoch 0.9.18 → RUSTSEC-2026-0204, fix >=0.9.20; anyhow 1.0.102
unsound RUSTSEC-2026-0190).

Verified: actionlint exit 0; matrix has 1 `actions` leg, 0 active `rust` legs.

Part of the estate-wide CI cleanup: 13 repos carry this beta-Rust CodeQL leg.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Author: hyperpolymath

.github/workflows/codeql.yml

@@ -38,8 +38,6 @@ jobs:
           # the prior matrix as containing no language present in the repo.
           - language: actions
             build-mode: none
-          - language: rust
-            build-mode: none
 
     steps:
       - name: Checkout