Add CI gates for Swift, Rust, Studio, validation, and benchmark smoke

[DennisWayo]

Problem Statement

SchroSIM is already positioned as reproducible research software, but the main CI workflow only builds the Python source distribution, checks package metadata, installs the package, and runs schrosim --help. That misses the Swift simulator, the SwiftUI Studio target, the Rust runtime, cross-runtime validation, trace SLOs, and benchmark smoke gates described in the developer docs.

Proposed Solution

Expand .github/workflows/ci.yml into a real public confidence gate:

• macOS Swift job: bash scripts/swift-test.sh, swift build --product schrosim-cli, swift build --product schrosim-studio, swift run schrosim-cli version.
• Rust job: cargo test -p schrosim-core, cargo run -q -p schrosim-core -- version.
• Validation job: bash scripts/cv-validation-suite.sh --runtime both and bash scripts/trace-slo-check.sh --max-gates 512 --max-frame-ms 50.
• Benchmark smoke job with a short compute-benchmark.sh run and explicit p95 budget.

Acceptance Criteria

• Pull requests fail if Swift tests, Rust tests, Studio build, validation suite, or trace SLO fail.
• CI uploads validation and benchmark JSON outputs as artifacts.
• CI status names are stable enough to become branch protection checks.
• The developer guide points to the workflow instead of describing this as a mostly manual release preflight.

Validation

bash scripts/swift-test.sh
cargo test -p schrosim-core
bash scripts/cv-validation-suite.sh --runtime both
bash scripts/trace-slo-check.sh --max-gates 512 --max-frame-ms 50

Evidence

• .github/workflows/ci.yml
• docs/13-developer-guide.md
• docs/09-validation-and-benchmarks.md