feat: add CLI source config tags

[XXPermanentXX]

Summary

• add product and version dimensions to x-dashscope-source-config
  • t1=public
  • t2=bl|kscli
  • t3=<CLI version>
• inject source metadata at Bailian/DashScope API boundaries while excluding OSS uploads, result downloads, transcription downloads, and update checks
• document the current backend channel identifiers and AEM command telemetry flow

Why

Gateway-side consumption needs to distinguish Bailian CLI from Knowledge Studio CLI and attribute requests to the actual product version without propagating channel metadata through generic network transfers.

Impact

• bl and kscli requests can be segmented by product and version
• existing User-Agent behavior is preserved
• AEM command telemetry behavior is unchanged
• generic OSS/npm/download traffic no longer receives x-dashscope-source-config

Validation

• git diff --check
• vp check — 0 errors; 3 pre-existing warnings
• vp test packages/core/tests/instrumented-fetch.test.ts packages/core/tests/index.test.ts — 21/21 passed