feat(spark): add iFLYTEK Spark model provider

[FenjuFu]

Description

Adds iFLYTEK Spark (讯飞星火) as a model provider. Spark is one of the major
Chinese foundation models still missing from Continue (DeepSeek, MiniMax,
Moonshot, MiMo, zAI and others are already supported), so this fills that gap.

Spark exposes an OpenAI-compatible HTTP endpoint at
https://spark-api-open.xf-yun.com/v1 authenticated with a single Bearer API
Password, so the provider is a thin OpenAI wrapper — the same shape as the
recently merged MiniMax provider (#11367).

Wired up end to end, mirroring the MiniMax addition:

• core/llm/llms/Spark.ts + registration in core/llm/llms/index.ts
• packages/openai-adapters/src/apis/Spark.ts + index.ts case + types.ts config schema
• packages/llm-info/src/providers/spark.ts + index.ts (model metadata for the 6 public models)
• packages/config-types provider enum + core/llm/autodetect.ts (templating / parallel lists)
• GUI add-model config (gui/src/pages/AddNewModel/configs/{models,providers}.ts)
• Docs page + overview table row

Default model is 4.0Ultra; generalv3.5 (Max), max-32k, generalv3 (Pro),
pro-128k and lite are also selectable.

Checklist

• I've read the contributing guide
• The relevant docs, if any, have been updated or created
• The relevant tests, if any, have been updated or created

Tests

No unit tests were added — this follows the same pattern as the existing MiniMax
provider (which ships as a config-only OpenAI-compatible wrapper). Happy to add
coverage under packages/openai-adapters if you'd prefer. I wasn't able to run
the full monorepo build/lint locally; flagging so CI can validate formatting.

Notes

• The apiKey is the API Password for the Spark HTTP service
  (http服务接口认证信息 → APIPassword in the console), distinct from the
  APPID/APIKey/APISecret triple used by Spark's legacy WebSocket API.

[github-actions]

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[FenjuFu]

I have read the CLA Document and I hereby sign the CLA