Moonshot provider owns chat impl; video input supported

Patch Changes

• b283a6f: feat(provider/moonshotai): own the chat implementation, support video input. The provider no longer builds on @ai-sdk/openai-compatible; the converter, language model, and helpers are owned by the package. Video file parts (e.g. mediaType: 'video/mp4') are converted to Moonshot's video_url content parts for video-capable models (kimi-k3, kimi-k2.7-code, kimi-k2.6, kimi-k2.5). Audio and PDF file parts now throw client-side (the API rejects those part types). reasoningHistory: 'preserved' now maps to Moonshot's thinking.keep: 'all' request field (previously a no-op, the API ignores reasoning_history), gated per model with a warning on models without thinking.keep support. Adds promptCacheKey and safetyIdentifier provider options, widens reasoningEffort to 'low' | 'high' | 'max' per Moonshot's docs, maps the generic reasoning call option to reasoning_effort, and passes ms:// Files API references through natively (declared in supportedUrls).