ci: stop auto-running PR Quick

[SunSi12138]

Summary

• make PR Quick manual-only again
• move the package/Quick Start validation introduced by docs: make README NuGet-first with runnable templates #608 into a dedicated PR Package Smoke workflow
• keep the same package/doc/source path coverage without re-running integration, AOT, demos, load smoke, and chaos on ordinary PRs

Why

PR Fast is already the normal pull-request gate. #608 re-added a path-filtered pull_request trigger to PR Quick for package documentation validation, which causes core Client/Server changes to run both Fast and the full legacy Quick workflow.

The dedicated package-smoke workflow keeps the intended fresh-package consumer validation while removing the duplicate full gate.

Validation

• branch is based directly on current dev
• PR Quick retains workflow_dispatch and its full validation sequence
• PR Package Smoke runs only for the package/doc/source paths previously attached to PR Quick
• PR Fast remains unchanged and continues to run on normal PR activity

[SunSi12138]

复审通过，未发现 correctness / CI-gate blocker。PR Quick 改为仅 workflow_dispatch 后仍保留完整 quick + codec compatibility；新的 PR Package Smoke 承接原自动 Quick 中的 build/pack/package-contract/package-consumer/Quick Start 验证，并已在 exact head 上成功运行。当前 dev ruleset 只要求稳定 context fast，因此移除 Quick 的自动 PR trigger 不会制造 required-check 死锁。PR head 与当前 dev 同步（behind 0），可按 exact head squash 合并。