Fixes #39684 - Scope Puppet autocomplete by taxonomy

[jakduch]

Summary

Fixes #39684 as a follow-up to foreman_puppet #450.

The custom Puppet assignment completer queried classes and config groups globally, bypassing the current organization and location scope of the host or host group being searched. Restrict its assignment subqueries to host and host group Puppet facets visible in the active taxonomies. Direct assignments, inherited host group assignments, and assignments through config groups remain available.

Testing

• Ruby syntax checks pass for all changed files
• git diff --check passes
• Regression coverage verifies organization scoping for host completions and location scoping for host group completions
• Coverage includes both Puppet class and config group values
• Full Rails tests are left to CI

AI usage disclosure

Per the community discussion on AI policy, the issue was investigated and the changes, tests, and PR wording were prepared with the assistance of Codex 5.6 Sol High. The resulting changes were reviewed before submitting. The commit also includes an Assisted-By trailer.