[Chore] Speed up CI dependency setup

[openroomote-bruno]

​Created by Roomote. View the task or mention @roomote for follow-up asks.

What changed

Frontend CI now fingerprints the Bun lockfile, manifest, .nvmrc, and any explicit Node version override in its dependency cache key. Jobs skip bun install --frozen-lockfile on an exact cache hit while continuing to reinstall after partial or missing restores.

Why this change was made

The CI setup restored node_modules but still reinstalled dependencies in every frontend job, repeating work across the test and build matrix. The cache remains centralized and immutable, and cache misses retain the existing frozen install path for correctness.

Impact

A warm exact cache removes the dependency-install step from each frontend job, expected to save roughly 1-3 minutes per frontend job and reduce aggregate PR CI time by several minutes across the matrix. Cache invalidation now follows dependency and runtime changes, avoiding unsafe reuse of native modules. Workflow-level cancellation for superseded PR runs was reviewed but left for follow-up because this delivery credential cannot modify .github/workflows; the push was rejected when that permission was required. YAML formatting checks and git diff --check passed. Full GitHub Actions linting was unavailable locally because actionlint and yamllint are not installed.