Move company import/export to dedicated pages with file-browser UX

- Add /:company/company/export page with file tree, checkboxes for
  per-file selection, and read-only preview pane (skills-style layout)
- Add /:company/company/import page with source form (GitHub/URL/local),
  target/collision settings, preview tree with action badges, and detail pane
- Add Import/Export buttons to the Org Chart page header
- Replace import/export sections in CompanySettings with redirect links
- Clean up ~800 lines of dead code from CompanySettings
- Register new routes in App.tsx

Co-Authored-By: Paperclip <noreply@paperclip.ing>
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

ui/src/App.tsx

@@ -23,6 +23,8 @@ import { Activity } from "./pages/Activity";
 import { Inbox } from "./pages/Inbox";
 import { CompanySettings } from "./pages/CompanySettings";
 import { CompanySkills } from "./pages/CompanySkills";
+import { CompanyExport } from "./pages/CompanyExport";
+import { CompanyImport } from "./pages/CompanyImport";
 import { DesignGuide } from "./pages/DesignGuide";
 import { InstanceSettings } from "./pages/InstanceSettings";
 import { PluginManager } from "./pages/PluginManager";
@@ -115,6 +117,8 @@ function boardRoutes() {
       <Route path="onboarding" element={<OnboardingRoutePage />} />
       <Route path="companies" element={<Companies />} />
       <Route path="company/settings" element={<CompanySettings />} />
+      <Route path="company/export" element={<CompanyExport />} />
+      <Route path="company/import" element={<CompanyImport />} />
       <Route path="skills/*" element={<CompanySkills />} />
       <Route path="settings" element={<LegacySettingsRedirect />} />
       <Route path="settings/*" element={<LegacySettingsRedirect />} />