fix(ci): drop beta-Rust CodeQL leg (cancelled/hanging 'checks 2 things forever') (#60)

## What

The CodeQL matrix analysed a `rust` leg. **CodeQL Rust support is beta**
— that leg cancels/hangs and never resolves (the recurring *"CodeQL
checks 2 things forever"* symptom), providing zero real security
coverage.

## Fix

Remove the `rust` leg; keep/ensure an `actions` leg so the matrix stays
non-empty (no zero-jobs `startup_failure`). Rust security belongs in
native tooling (cargo-audit / clippy), not beta CodeQL.

## Verification

`actionlint`: no parse/syntax errors; matrix has an `actions` leg and
zero active `rust` legs.

## Context

Estate-wide shared-fate: 13 repos carried this beta-Rust CodeQL leg.
Reference: hyperpolymath/gitbot-fleet#375.

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

Co-authored-by: Claude Fable 5 <noreply@anthropic.com>

Author: hyperpolymath

.github/workflows/codeql.yml

@@ -48,8 +48,6 @@ jobs:
           build-mode: none
         - language: javascript-typescript
           build-mode: none
-        - language: rust
-          build-mode: none
         # CodeQL supports the following values keywords for 'language': 'actions', 'c-cpp', 'csharp', 'go', 'java-kotlin', 'javascript-typescript', 'python', 'ruby', 'rust', 'swift'
         # Use `c-cpp` to analyze code written in C, C++ or both
         # Use 'java-kotlin' to analyze code written in Java, Kotlin or both