Add shared package: types, schemas, plans and API client

Holds everything web, mobile and API must agree on: DTOs, zod input
schemas, plan entitlements (the single place feature gates live),
streaming-service link helpers, feed ordering and a typed API client.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01MzFywujuH9TiuXbr9vjoX8

packages/shared/src/index.ts

@@ -0,0 +1,6 @@
+export * from './services';
+export * from './dto';
+export * from './schemas';
+export * from './plans';
+export * from './client';
+export * from './time';