Settings-app refinement round 2 (owner review): toggle fix, shared model dropdown, groups, graph-view graying, pruned hints

- Toggle knob (bug report): the knob span had no left anchor, so it sat
  at its inline static position — right-edge in off, overflowing in on.
  Now left-0 + the intended 2px/18px translate; verified live: 3px from
  left when off, 1px right inset both states.
- Role model/thinking dropdowns (owner ask): the EXACT chat model
  selector dropdown, not a lookalike — the fuzzy-search + arrow-walk +
  Enter machine moved from model-picker.tsx into the shared
  components/settings/model-menu.tsx (ModelMenuList/ThinkingMenuList),
  ModelControl now renders the same bodies, and the agent roles open
  them downward with a pinned Default row (clears the override). The
  collapsed trigger keeps the thin select look (owner: 'the collapsed
  look is good'). Esc claims and closes only the menu (the dialog
  stays); a backdrop click is left to the dialog's own close.
- Sub-groups (owner ask): SettingsGroup — Models / Tools / System
  prompts inside Agent, each with a separator + quiet label; section
  headings more pronounced (text-sm, full-foreground).
- Graying (owner ask): graph-view render-panel convention — the WHOLE
  row dims (opacity-40) and the control locks; the row owns the dim so
  no double-opacity. Applied to the graph ladder, the mode row, and
  prompt rows without an override file. The 'needs X on' prose is gone.
- Hints pruned (owner ask): mechanics-explaining lines removed — the
  ladder mention, 'App-level behavior', 'Applied live as CSS
  variables', per-row explanations. Only the keyboard storage note
  stays, reworded 'Stored on this device' (desktop app — localStorage
  is the Chromium profile in Application Support, not 'this browser').

Live-verified: knob geometry both states + PUT round-trip, menu
search/pick/clear through the record, thinking set/clear, Esc layering,
ladder dim 0.4 with siblings full, pruned phrases absent. Gates:
typecheck, lint, 701/701.

components/settings/keyboard-section.tsx

@@ -155,7 +155,7 @@ export function KeyboardSection() {
 				);
 			})}
 			<div className="mt-1 flex items-center justify-between">
-				<span className="text-xs text-muted-foreground/70">Stored in this browser (lh:keymap) — overrides only.</span>
+				<span className="text-xs text-muted-foreground/70">Stored on this device (lh:keymap) — overrides only.</span>
 				<button
 					type="button"
 					onClick={resetAll}