Improve CI caching and reliability coverage

[DjDeveloperr]

Summary

• split CI into parallel Rust, client, package, build-artifact, and integration jobs with Cargo/npm caching
• add cached SwiftUI integration fixture builder shared by CLI and JS API integration suites
• expand deterministic Rust unit coverage for native bridge parsing, WebRTC lifecycle/timing, API accessibility/inspector logic, config, and metrics
• add an opt-in stress/leak runner for live daemon reliability checks

Validation

• npm test
• cargo clippy --manifest-path server/Cargo.toml --all-targets -- -D warnings
• npm run --prefix client typecheck
• npm run build:client
• npm run build:packages
• npm run package:vscode-extension
• npm run test:integration:fixture
• node --check scripts/integration/fixture.mjs && node --check scripts/integration/prebuild-fixture.mjs && node --check scripts/integration/cli.mjs && node --check scripts/integration/js-api.mjs && node --check scripts/stress/simdeck.mjs
• npx prettier --check package.json .github/workflows/ci.yml docs/guide/testing.md scripts/integration/fixture.mjs scripts/integration/prebuild-fixture.mjs scripts/integration/cli.mjs scripts/integration/js-api.mjs scripts/stress/simdeck.mjs
• cargo fmt --manifest-path server/Cargo.toml --check
• git diff --check
• CI YAML parse check