Extend no-skip enforcement to the unit vitest config

[coderdan]

The integration vitest config fails the run if any test is skipped
(packages/stack/integration/no-skips-reporter.ts), on the principle that a
skipped test reads exactly like a passing one and every silent coverage hole this
project has found took that shape. The unit config
(packages/stack/vitest.config.ts) has no such guard.

Goal

Wire the no-skips reporter (or an equivalent) into the unit vitest config so a
.skip/.skipIf/.todo in the unit suite fails CI.

Prerequisite: eliminate or justify the remaining unit skips

The unit run currently reports a handful of skipped tests (~5 last observed), so
turning the guard on today would go red. Before enabling it:

• Audit the remaining describe.skip/it.skip/skipIf in packages/stack/__tests__/**.
• For each, either make it run unconditionally and throw loudly when
  unconfigured (the model the integration suites and the LIVE_* gate removal
  already adopted), or move it to the integration suite if it genuinely needs a
  database/PostgREST.
• Note the credential-gated cases: some suites need CS credentials or
  DATABASE_URL and currently skip when absent — decide per suite whether they
  belong in unit (throw loudly, CI provides creds) or integration.

Done when

• No .skip/.todo survives in the unit suite (or each is converted to a loud throw / relocated).
• The unit vitest config runs the no-skips reporter and a stray skip fails CI.

Context: session follow-up on the 1.0 candidate (#535); mirrors the integration
suite's loud-failure model.