The left-nav Skills pane and Settings > Skills & Tools rendered the same
getSkills()/getToolsets() data with the same helpers and toggles — genuine
duplication that drifted (different default category labels, sort orders).
Make the left pane the single home: it keeps its category-tabbed browsing
and now gains the functional bits it lacked — a real toolset enable/disable
switch (was a read-only pill) and the expandable ToolsetConfigPanel for
provider selection + per-key credential config. Remove the Tools section
from Settings (nav item, view branch, query slot, type union entries) and
delete tools-settings.tsx, migrating its toggle coverage into the skills
pane test. Relabel the entry point to 'Skills & Tools' in the sidebar and
command center.