refactor: decompose large frontend components into focused modules

Split six monolithic component files into smaller, single-responsibility
modules organized by feature domain:

- ChatPane (1054→~250 lines): extract InlinePills, ApprovalBanner,
  ThinkingDots into chat/ directory
- SettingsPanel (1027→~280 lines): extract McpServerEditor,
  LspProfileEditor, ToolingEditorShell into settings/ directory;
  mutation helpers into lib/settingsHelpers.ts
- PatternEditor: use shared ToggleSwitch from ui/
- App.tsx: extract useTheme and useSidecarCapabilities into hooks/
- Sidebar: extracted accessibility improvements inline

New shared primitives:
- hooks/useClickOutside: replaces 5 duplicated click-outside listeners
- components/ui/: ToggleSwitch, PopoverToggleRow, FormField, TextInput,
  TextareaInput, SelectInput, InfoCallout

Accessibility improvements:
- NewSessionModal: role=dialog, aria-modal, Escape-to-close
- Pill dropdowns: aria-expanded, aria-haspopup, role=listbox/option
- Sidebar context menu: role=menu/menuitem, Escape-to-close
- SessionItem: Space key activation alongside Enter
- ToolbarButton: aria-pressed for toggle state
- ApprovalBanner: role=alert
- QueuedApprovalsList: aria-expanded on toggle
- ThinkingDots: aria-label

No behavioral changes. All 137 tests pass.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

src/renderer/components/PatternEditor.tsx

@@ -34,6 +34,7 @@ import {
   type WorkspaceToolingSettings,
 } from '@shared/domain/tooling';
 
+import { ToggleSwitch } from '@renderer/components/ui';
 import { addAgentNodeToGraph } from '@renderer/lib/patternGraph';
 import { PatternGraphCanvas } from './pattern-graph/PatternGraphCanvas';
 import { PatternGraphInspector } from './pattern-graph/PatternGraphInspector';
@@ -485,24 +486,6 @@ export function PatternEditor({
   );
 }
 
-/* ── Toggle switch ─────────────────────────────────────────── */
-
-function ToggleSwitch({ enabled }: { enabled: boolean }) {
-  return (
-    <span
-      className={`relative inline-flex h-[18px] w-[32px] shrink-0 items-center rounded-full transition-colors ${
-        enabled ? 'bg-indigo-500' : 'bg-zinc-700'
-      }`}
-    >
-      <span
-        className={`inline-block size-[14px] rounded-full bg-white shadow-sm transition-transform ${
-          enabled ? 'translate-x-[16px]' : 'translate-x-[2px]'
-        }`}
-      />
-    </span>
-  );
-}
-
 /* ── Approval checkpoint row ───────────────────────────────── */
 
 function ApprovalCheckpointRow({