feat(categories): detail page with fleet insights

Clicking a category anywhere in the app now opens /categories/:id with
MPN breakdown, manufacturer mix, failures by MPN, and past-EOL exposure
— a dual of the manufacturer detail page.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

apps/web/src/App.tsx

@@ -16,6 +16,7 @@ import Manufacturers from './pages/Manufacturers.js';
 import ManufacturerDetail from './pages/ManufacturerDetail.js';
 import PartModels from './pages/PartModels.js';
 import PartModelDetail from './pages/PartModelDetail.js';
+import CategoryDetail from './pages/CategoryDetail.js';
 import Fms from './pages/Fms.js';
 import FmDetail from './pages/FmDetail.js';
 import Repairs from './pages/Repairs.js';
@@ -66,6 +67,7 @@ export default function App() {
                     <Route path="/manufacturers/:id" element={<ManufacturerDetail />} />
                     <Route path="/part-models" element={<PartModels />} />
                     <Route path="/part-models/:id" element={<PartModelDetail />} />
+                    <Route path="/categories/:id" element={<CategoryDetail />} />
                     <Route path="/fms" element={<Fms />} />
                     <Route path="/fms/:id" element={<FmDetail />} />
                     <Route path="/repairs" element={<Repairs />} />