chore(types): widen UseCase.category from union to string (#13)

Future use-case category additions in InstaNode-dev/content/use-
cases.json now ship without a dashboard PR. The closed A–I union
was useful as documentation but its rigidity meant every new
category (J, K, L, …) would need a coordinated dashboard change
just to satisfy the type checker, even though the runtime behavior
(group by string, render alphabetically) is identical.

This is the last shape change to useCases.ts for category growth.
The content repo is now the source of truth for what categories
exist on /use-cases.

Verified: build still produces 104 cards across 18 categories in
dist/use-cases/index.html after the upstream content commit added
the parallel-agent J–R cases.

Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: mastermanas805

src/content/useCases.ts

@@ -11,16 +11,13 @@
 
 export type Service = 'pg' | 'redis' | 'mongo' | 'nats' | 'minio' | 'webhook' | 'deploy'
 
-export type Category =
-  | 'A. AI coding agents'
-  | 'B. Multi-agent systems'
-  | 'C. Vertical AI apps'
-  | 'D. Personal AI'
-  | 'E. Browser & automation agents'
-  | 'F. Developer tooling'
-  | 'G. Internet-of-AI'
-  | 'H. Indie & SaaS founders'
-  | 'I. Hackathon & education'
+/* Category is intentionally a plain string. The content repo is the source
+ * of truth for what categories exist, so the dashboard should accept
+ * anything that lands there. The UseCasesPage renders categories in
+ * alphabetical order and uses them as filter-chip labels — no code path
+ * needs a closed union. Adding a new category = one entry in
+ * use-cases.json; no dashboard PR. */
+export type Category = string
 
 export type UseCase = {
   title: string