refactor(core-trpc): break the core-api package cycle

core-trpc imported AppRouter (type-only) from core-api, which depends
on the features, which depend on core-trpc — a cycle that killed every
turbo graph walk (lint/build/CI) and an illegal core -> core-composition
boundary edge. The tRPC context is now router-agnostic (AnyTRPCRouter);
useTRPC takes the router type as a generic and each feature exports a
type-only app-slice (e.g. BlogAppSlice) mirroring its mount key, so UI
hooks keep full procedure typing without touching the composition layer.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

packages/core-trpc/src/providers/next-provider.tsx

@@ -4,7 +4,7 @@ import { useState } from "react";
 import { QueryClientProvider } from "@tanstack/react-query";
 import { createTRPCClient, httpBatchLink } from "@trpc/client";
 import superjson from "superjson";
-import type { AppRouter } from "@repo/core-api";
+import type { AnyTRPCRouter } from "@trpc/server";
 import { TRPCProvider } from "../client";
 import { getQueryClient } from "../query-client";
 
@@ -22,7 +22,9 @@ export function NextTrpcProvider({
 }) {
   const [queryClient] = useState(() => getQueryClient());
   const [trpcClient] = useState(() =>
-    createTRPCClient<AppRouter>({
+    // Router-agnostic on purpose: procedure typing comes from useTRPC<TRouter>
+    // at the call sites, not from the wire-level client.
+    createTRPCClient<AnyTRPCRouter>({
       links: [
         httpBatchLink({
           url: `${getBaseUrl()}${trpcUrl}`,