[refactor] link sglang, lmdeploy and ROLL docs to official sites

[zheliuyu]

Summary

• Follow-up to [RFC] Q3 2026 Refactoring Guide #135/[refactor] drop doc submodules, link community docs to official sites #136: stop building local install/quick-start pages for SGLang, LMDeploy, and ROLL, since upstream now hosts Ascend/NPU docs.
• Homepage cards and sidebar placeholders now point to the official GitHub, docs hub, and Ascend guide for each project.
• llama.cpp is unchanged and still built locally.

Test plan

• make html succeeds
• Homepage cards for sglang / lmdeploy / ROLL open the correct official pages
• Sidebar placeholder pages list the same three links
• llama.cpp still shows local install and quick start

[ascend-robot]

CLA Signature Pass

zheliuyu, thanks for your pull request. All authors of the commits have signed the CLA. 👍

[zheliuyu]

Test plan