Re-enable flaky E2E tests disabled in #8936

## Context

PR #8936 disabled 5 flaky E2E test suites that intermittently fail on slow CI runners due to timing issues:

- `packages/prover/test/e2e/cli/cmds/start.test.ts` — hook timeout (shared env finalization)
- `packages/prover/test/e2e/web3_provider.test.ts` — same
- `packages/prover/test/e2e/web3_batch_request.test.ts` — same
- `packages/beacon-node/test/e2e/api/impl/lightclient/endpoint.test.ts` — event timeout
- `packages/beacon-node/test/e2e/chain/lightclient.test.ts` — DB race condition

## Root Causes

1. **Prover tests**: `minFinalizedTimeMs` is too tight for slow CI runners. Docker container startup adds 30-90s variable overhead.
2. **Lightclient endpoint**: Event wait and test timeout too short for slow block production.
3. **Lightclient track head**: `bn.db.block.get(headRoot)` returns null when block is still in the write pipeline.

## To Re-enable

Fix the underlying timing issues in the shared E2E test environment, then remove the `describe.skip` wrappers.