Revert "chat: disable progress border by default" #343337

Reverts #342958.

Motivation

Per standup feedback, keep the glowing progress border enabled by default until the sticky progress indicator is finalized.

Change

Restore the default of chat.progressBorder.enabled from false to true. This is the exact inverse of commit 23e257a3daed3f3d59498fe88f128ca59cdff592; explicit user settings and the existing reduced-motion handling remain unchanged.

Validation

• 
  git diff HEAD^ HEAD --check - passed.


• A dependency-free Node assertion verified that the only changed file and changed lines exactly reverse #342958 and that the registered default is true - passed.


• 
  npm run eslint -- src/vs/workbench/contrib/chat/browser/chat.shared.contribution.ts - could not run: ERR_MODULE_NOT_FOUND for the uninstalled eslint package.


• Full build, unit tests, and manual UI checks were not run for this one-line default restoration.

How to Test

In a fresh profile, confirm that chat.progressBorder.enabled is enabled by default and that an agent request displays the animated progress border. Set it to false to confirm the opt-out still works, and enable reduced motion to confirm the animated border remains suppressed.