Tests optimizations #35327

Measured CI critical path across BC Registries repos (latest green run of each). Goal: cut PR feedback time without reducing coverage.

Done (PR bcgov/business-dashboard-ui#303): Cypress 6m33s to 2m55s via 3 shards, removed hard sleeps, stubbed LaunchDarkly / state filing / external navigations, flaky-attempt logger.

Remaining work, ranked by payoff:

1. lear legal-api pytest: 13 min single process. Shard-ready (testcontainers Postgres, session DB, nested-transaction rollback per test, no serial marks). Split into 3 matrix jobs (services / resources / rest) with coverage merge, or pytest-xdist with per-worker DB. Target ~4 min. Needs a shard input in bcregistry-sre backend-ci.yaml or a lear-local workflow.
2. bcregistry-sre frontend-ci.yaml: npx nuxt prepare runs on non-Nuxt apps (35-43s per job, 3 jobs per run) and the lint job gates unit tests and build. Guard nuxt prepare on nuxt.config presence, run lint in parallel with tests. Saves ~1.5 min on business-filings-ui, business-create-ui, business-edit-ui each. Owner: SRE.
3. business-ui corps Playwright: 158s on 1 shard. Matrix already supports --shard; set shardIndex: [1,2,3,4], shardTotal: [4] (currently commented out). Target ~60s.
4. bcrs-shared-components: uncached 88s npm install in each of 3 jobs. Add setup-node npm cache and npm ci. Saves ~1 min per job.
5. business-ui business-registry-ui vitest 126s. Review pool/isolation config, est. 30-50%.

Out of scope: filer, emailer, colin-api, Vue repo unit test configs (already reasonable).