fix(ai-chat): respect max_tokens parameter and model limit in MoonshotProvider

[Rajeev91691]

Fixes #3408

Summary

In MoonshotProvider.ts, complete() hardcoded max_tokens: 1000 when invoking the Moonshot API and ignored the max_tokens argument in ICompleteArguments.

Because thinking models like Kimi K3 perform internal reasoning steps before generating output text, they consume tokens during reasoning. With a hardcoded 1000-token limit, Kimi K3 exhausts its token budget during thinking and returns finish_reason: "length" with no output text.

Changes

• Destructured max_tokens from ICompleteArguments in MoonshotProvider.complete().
• Passed max_tokens: max_tokens || modelUsed.max_tokens || 1000 to allow caller-specified max_tokens while defaulting to the model's configured max token limit (modelUsed.max_tokens).
• Updated unit tests in MoonshotProvider.test.ts to verify max_tokens pass-through and fallback behavior.

Testing

Ran unit test suite via npm run test:backend:
✓ src/backend/drivers/ai-chat/providers/moonshot/MoonshotProvider.test.ts (22 tests passed)

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[Salazareo]

hi @Rajeev91691 could you sign the CLA?