Add test coverage for the SDK pool proving module

[collinsadi]

sdk/vitest.config.ts explicitly excludes src/prove/pool.ts from all coverage floors ("is 0% without them") and sets branches: 0 for prove/reputation.ts, so the SDK's proving core can regress without failing coverage.

Add fixture-based tests so the proving modules meet real thresholds.

Acceptance criteria:

• Pool and reputation proving have deterministic tests using committed fixtures.
• The per-file coverage exceptions are removed.
• CI records when artifact-dependent suites are skipped instead of passing silently.