feat(observability): report silent catalog UX degradations to Sentry

The catalog failures that hurt UX — a drill/parts fetch that fails into an empty
"couldn't load" panel, or a decoded vehicle whose category tree comes back empty
("model var ama parça yok") — all return HTTP 200 with a degraded body. Nothing
throws, so the global Sentry exception filter never sees them and they go
unnoticed (serkan's complaint was exactly this class). Report them explicitly.

- new common/catalog-degradation.ts: reportCatalogDegradation(kind, ctx),
  fingerprinted by kind+source+brand so each failure mode collapses into one
  countable Sentry issue (e.g. "drill-load-error · pl24/Ford — N events, M users").
- categories.service: capture on getCategoryWithParts loadError and on an empty
  getCategoryTree, Redis-deduped to <=1 event/hour per category/vehicle so a
  broken catalog can't flood the stream; telemetry never throws into the request.

tsc + biome clean, categories suite 10/10.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

apps/api/src/common/catalog-degradation.ts

@@ -0,0 +1,58 @@
+import * as Sentry from "@sentry/nestjs";
+
+/**
+ * A *silent* catalog UX failure: the request succeeds (HTTP 200) but the user
+ * gets a degraded result — an empty parts panel / retryable load error, or an
+ * empty category tree on a vehicle that decoded fine. Because nothing throws,
+ * the global exception filter never sees these, so they go unnoticed — exactly
+ * how serkan's "şase girdim, model var ama parça yok" sat invisible. We report
+ * them to Sentry explicitly so they surface and get triaged like real errors.
+ */
+export type CatalogDegradationKind =
+  | "empty-tree" // vehicle decoded but the category tree came back empty
+  | "drill-load-error"; // a category drill/parts fetch failed → empty/retry panel, not parts
+
+export interface CatalogDegradationContext {
+  vehicleId?: string | null;
+  vin?: string | null;
+  brand?: string | null;
+  model?: string | null;
+  source?: string | null;
+  categoryId?: string | null;
+  categoryName?: string | null;
+  linkPath?: string | null;
+}
+
+/**
+ * Send a catalog degradation to Sentry as a warning. Fingerprinted by
+ * kind + source + brand so every instance of one failure mode collapses into a
+ * single, countable Sentry issue ("drill-load-error · pl24/Ford — 1.2k events,
+ * 80 users") rather than thousands of unique events. Call sites must dedup
+ * (e.g. a short Redis TTL per vehicle/category) before invoking this, and must
+ * never let it throw into the request path.
+ */
+export function reportCatalogDegradation(
+  kind: CatalogDegradationKind,
+  ctx: CatalogDegradationContext,
+): void {
+  const source = ctx.source ?? "unknown";
+  const brand = ctx.brand ?? "unknown";
+  Sentry.captureMessage(`catalog degraded: ${kind} (${source}/${brand})`, {
+    level: "warning",
+    tags: {
+      catalog_degradation: kind,
+      catalog_source: source,
+      catalog_brand: brand,
+    },
+    // Group by failure mode, not by individual vehicle/category.
+    fingerprint: ["catalog-degradation", kind, source, brand.toLowerCase()],
+    extra: {
+      vehicleId: ctx.vehicleId ?? null,
+      vin: ctx.vin ?? null,
+      model: ctx.model ?? null,
+      categoryId: ctx.categoryId ?? null,
+      categoryName: ctx.categoryName ?? null,
+      linkPath: ctx.linkPath ?? null,
+    },
+  });
+}