Keep collection description edit action separate from description text

[VeiJitxiaoj]

Summary

• separate the collection description edit action from the rendered markdown body
• keep the rendered description as read-only content while using a dedicated Edit Description button
• preserve the existing markdown editor and preview behavior once editing starts

Verification

• git diff --check

Closes #34

[CLAassistant]

All committers have signed the CLA.

[VeiJitxiaoj]

Hi! The CLA is signed and the checks are passing now. Please let me know if any changes are needed.