custom and voice-crescendo strategies ignore an explicitly configured redteamProvider and use remote generation instead #10977

Describe the bug

The custom and voice-crescendo red-team strategies have the same provider substitution defect as #10970 (fixed for iterative/crescendo in #10972): when remote generation is enabled, an explicitly configured redteamProvider is silently replaced with Promptfoo's cloud API.

In src/redteam/providers/custom/index.ts, both provider accessors take the remote path whenever shouldGenerateRemote() is true, even though the local branches were written to honor the config:

private async getRedTeamProvider(): Promise<ApiProvider> {
    if (!this.redTeamProvider) {
      if (shouldGenerateRemote()) {
        this.redTeamProvider = new PromptfooChatCompletionProvider({ task: 'crescendo', ... });
      } else {
        this.redTeamProvider = await redteamProviderManager.getProvider({
          provider: this.config.redteamProvider,   // honored only when remote is disabled
          ...
        });
      }
    }

getScoringProvider in the same file has the identical shape, and src/redteam/providers/voiceCrescendo/index.ts repeats it in getRedTeamProvider. The consequences are the ones #10970 enumerated: the attacker (and for custom, the judge) runs on a different model than configured, prompts and outputs leave the machine to api.promptfoo.app, and nothing is logged about the swap.

Expected behavior

Same rule #10972 established: remote generation is only for the default, unconfigured case. With an explicit redteamProvider, both strategies should keep the attacker (and custom's scorer) local, i.e. gate the remote branch on shouldGenerateRemote() && !this.config.redteamProvider.

Scope notes

• hydra is not affected: it requires remote generation by design and throws a clear error otherwise (the GOAT class in Iterative and Crescendo strategies ignore an explicitly configured redteamProvider and use remote generation instead #10970's terms).
• iterativeTree receives its attacker provider by injection; its shouldGenerateRemote() call sites only gate input materialization, not provider selection.
• voiceCrescendo's getScoringProvider deliberately omits the config on the local path too ("let getGradingProvider check CLI --grader first"), so it is out of scope here.

I have the patch and regression tests ready, mirroring #10972's guard and test pattern; happy to open the PR.

System information

Reproduced by inspection on current main (f385d96), cross-checked against the #10972 diff; the code paths above are identical in shape to the pre-fix iterative/crescendo ones and diverge only in task id. promptfoo 0.123.0, macOS arm64, Node 22.