[codex] fix: clarify Cursor CLI setup error

[StiensWout]

Summary

• Add the Cursor CLI installation docs link to the missing Cursor CLI command status.
• Clarify Cursor ACP discovery failures with setup guidance while keeping the server-log hint.
• Keep the provider behavior unchanged; this only adjusts status copy and the matching exact-message assertion.

Root cause

Cursor setup failures used terse or stale copy: the command-missing status hard-coded the old command wording without the install docs, and ACP discovery failures only told users to check server logs.

Impact

Users who need to install or enable the Cursor CLI now get the installation URL directly in the provider status, and ACP discovery failures explain that Cursor CLI setup may be incomplete before falling back to server-log details.

Validation

• PATH="$HOME/.vite-plus/bin:$PATH" vp test apps/server/src/provider/Layers/CursorProvider.test.ts
• PATH="$HOME/.vite-plus/bin:$PATH" vp check
• PATH="$HOME/.vite-plus/bin:$PATH" vp run typecheck

Refs pingdotgg#2847