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>

packages/shared/src/category-insights.ts

@@ -0,0 +1,49 @@
+export interface CategoryPriceStats {
+  total: number;
+  average: number;
+  min: number | null;
+  max: number | null;
+  countWithPrice: number;
+}
+
+export interface CategoryFailureStats {
+  repairs: number;
+  distinctFailedParts: number;
+  fmsImplicating: number;
+}
+
+export interface CategoryManufacturerCount {
+  manufacturerId: string;
+  manufacturerName: string;
+  count: number;
+}
+
+export interface CategoryModelCount {
+  partModelId: string;
+  mpn: string;
+  count: number;
+}
+
+export interface CategoryModelFailureCount {
+  partModelId: string;
+  mpn: string;
+  repairs: number;
+}
+
+export interface CategoryPastEolModel {
+  partModelId: string;
+  mpn: string;
+  eolDate: string;
+  deployedCount: number;
+}
+
+export interface CategoryInsights {
+  totalPartModels: number;
+  totalParts: number;
+  priceStats: CategoryPriceStats;
+  failures: CategoryFailureStats;
+  byManufacturer: CategoryManufacturerCount[];
+  topModelsByUnits: CategoryModelCount[];
+  failuresByModel: CategoryModelFailureCount[];
+  pastEolModels: CategoryPastEolModel[];
+}

packages/shared/src/index.ts

@@ -20,3 +20,4 @@ export * from './csv-imports.js';
 export * from './analytics.js';
 export * from './part-model-insights.js';
 export * from './manufacturer-insights.js';
+export * from './category-insights.js';