aitools: make update-prune acceptance test hermetic

The update-prune acceptance test detected Claude Code (~/.claude), so
`aitools update` tried to migrate raw skills to the native databricks
plugin by shelling out to `claude plugin install`. The captured output
depended on whether `claude` was on the host PATH: developer machines
with claude installed recorded the marketplace "install-failed" error,
while CI runners (no claude) produced a "cli-not-on-path" error, so the
golden diverged and the build job failed on every platform.

Detect Cursor instead, a skills-only agent with no databricks plugin, so
update exercises the raw-skill prune path (the test's actual subject)
without touching any plugin-capable agent's CLI. The plugin migration
path is already covered hermetically by unit tests in cmd/aitools.

The test now passes with or without claude on PATH.

Co-authored-by: Isaac

Author: simonfaltum

acceptance/experimental/aitools/skills/update-prune/output.txt

@@ -3,7 +3,7 @@
 >>> [CLI] experimental aitools install --skills-only --global
 Command "install" is deprecated, use "databricks aitools install" instead.
 Flag --global has been deprecated, use --scope=global
-Installing Databricks skills for Claude Code...
+Installing Databricks skills for Cursor...
 Using skills version test-ref
 Fetching skills manifest...
 Downloading alpha...
@@ -15,8 +15,6 @@ Installed 2 skills.
 === update against a release where beta is gone: alpha updates, beta is pruned
 >>> DATABRICKS_SKILLS_REF=v2-ref [CLI] experimental aitools update --scope global
 Command "update" is deprecated, use "databricks aitools update" instead.
-Installing databricks plugin for Claude Code...
-Skipped Claude Code: claude-code: install-failed: ✘ Failed to install plugin "databricks@claude-plugins-official": Plugin "databricks" not found in marketplace "claude-plugins-official". Your local copy may be out of date — try `claude plugin marketplace update claude-plugins-official`.
 Downloading alpha...
 Exposing alpha to 1 agent...
   updated alpha v1.0.0 -> v2.0.0

acceptance/experimental/aitools/skills/update-prune/script

@@ -1,8 +1,12 @@
 # Isolate HOME: this test reconciles the whole install state, so it must not
 # share ~/.databricks with the sibling aitools acceptance tests.
 sethome home
-# Agent detection needs ~/.claude; prefer USERPROFILE on Windows.
-mkdir -p "${USERPROFILE:-$HOME}/.claude"
+# Detect Cursor, a skills-only agent (no databricks plugin), so update exercises
+# the raw-skill prune path without shelling out to a plugin-capable agent's CLI.
+# A plugin agent (e.g. Claude Code) would run `claude plugin install` during
+# update, making the output depend on whether `claude` is on the host PATH.
+# Prefer USERPROFILE on Windows.
+mkdir -p "${USERPROFILE:-$HOME}/.cursor"
 
 title "install two skills"
 trace $CLI experimental aitools install --skills-only --global