Define rust-packaged-path as the required CI health gate

[jununfly]

This was generated by AI during triage.

What to build

Define the existing cross-platform rust-packaged-path CI job as the required health gate for Rust indexing migration work. This should be an executable workflow contract, not a new heavy CI job.

Acceptance criteria

• The CI contract test verifies the rust-packaged-path job id and Rust packaged path (${{ matrix.os }}) job name.
• The contract verifies CI triggers on pull requests and pushes to main.
• The contract verifies the Linux, macOS, and Windows matrix, with fail-fast: false.
• The contract verifies Node 22, npm ci, npm run build, cargo test, and cargo build --package zcodegraph-core.
• The contract verifies Rust CLI engine path checks, SQLite/file-lock guardrails, and release artifact contract checks stay in the required gate.
• The contract verifies install-time Rust compilation remains absent from CI.
• CI naming or comments lightly communicate this job is the required health gate.
• Do not add a new CI job and do not add rust-package-smoke.mjs to PR CI.

Blocked by

None - can start immediately.

[jununfly]

This was generated by AI during triage.

Closing as implemented. The rust-packaged-path CI job is now documented and tested as the required Rust indexing health gate, without adding new CI jobs or moving package smoke into PR CI.

Verification: npx vitest run __tests__/ci-rust-packaged-path.test.ts; npx vitest run __tests__/release-workflow-rust-core.test.ts; git diff --check.