* feat: add trpc-fullstack skill for end-to-end type-safe API development
* fix: separate App Router and server-side context factories per review feedback
- Replace createContext({ req } as any) in App Router handler with
createTRPCContext(opts: FetchCreateContextFnOptions) — the correct fetch adapter shape
- Add createServerContext() for Server Component callers so auth() is called
directly without an empty or synthetic request object cast
- Update SSR example to use createServerContext() instead of createContext({} as any)
- Add two new pitfall entries covering both auth failure scenarios
