- Remove unused imports (importlib, sys in api/plugins.py; pytest in test).
- Two tests asserted 'X or True' (always pass — meaningless). Rewrote them to
actually verify the /plugins/ route allowlists plugin.css + uses relative_to
traversal guard, and that manifest fields are html.escape()'d before IIFE-shell
interpolation. Dropped a dead 'original_plugins' local for a real dict assertion.
