perf: keep affected coverage on CI

[thymikee]

Summary

Keep coverage visible in the affected-check plan, but make it GitHub-authoritative instead of running LCOV in the local pre-push loop.

Run plain Vitest related tests locally and deduplicate the full unit/provider aggregates. Remove the special affected-coverage command path and document the faster feedback-loop contract.

Validation

• pnpm check:affected:test (47 tests passed)
• pnpm check:affected --run (full fail-open selector/tooling plan passed in about 2 minutes)
• Coverage remains reported as GitHub-authoritative (Coverage job)

[github-actions]

Size Report

Metric	Base	Current	Diff
JS raw	2.33 MB	2.33 MB	0 B
JS gzip	765.0 kB	765.0 kB	0 B
npm tarball	888.6 kB	888.6 kB	0 B
npm unpacked	3.10 MB	3.10 MB	0 B

Startup median (7 runs, lower is better):

Scenario	Base	Current	Diff
CLI --version	27.1 ms	30.5 ms	+3.3 ms
CLI --help	68.6 ms	70.6 ms	+2.1 ms

Top changed chunks: no changes in the largest emitted chunks.

[thymikee]

Blocking: vitest-related now falls through to the unbounded generic command. The removed affected-coverage path deliberately applied DEFAULT_VITEST_MAX_WORKERS: broad vitest related spans configured projects, and default concurrency has already starved subprocess/provider tests beyond their fixed timeouts. This PR still runs that same related workload; removing LCOV instrumentation does not make the concurrency invariant obsolete.

Please retain the shared worker cap on the plain related command and assert it alongside the absence of coverage flags.