[TEST - DO NOT MERGE] Validate application catalog PR submission
仅新增验证说明文档，不修改应用列表或源码。用于验证 Hugging Face PR 投稿流程，自动飞书通知尚未启用，请勿合并。
Background
Create an explicitly labeled test pull request to verify the Hugging Face application catalog submission flow. Do not merge this test PR. Feishu integration for Hugging Face is currently deferred.
Changes
Add one validation note only. No application catalog entries or application source files are modified.
Protocol / API impact
None. The catalog, SDK, and runtime protocols remain compatible.
Configuration / secrets
None. No credentials, tokens, or local machine paths are committed.
Validation
Check the main revision and changed-file scope; read back the PR status and diff after creation. Robot runtime tests do not apply to this documentation change. This does not verify Feishu notification delivery from Hugging Face.
Risk and rollback
This adds a test item to the review queue. Do not merge it; close the PR after validation.
Test-only PR. The catalog submission flow was verified; this changes no application entry or source code. Closing without merge as part of test cleanup.