refactor(express): take messaging types from core

[Bccorb]

Closes #118

Problem

packages/express/src/messaging.ts and packages/core/src/authMessaging.ts were byte-identical, 114 lines each. Every messaging type was declared twice, and the two copies could drift without anything failing.

Change

Delete the express copy and point everything at @seamless-auth/core, matching the pattern already in src/index.ts for SeamlessUser, hasScopedRole, and roleGrantsAccess:

• src/index.ts: the messaging type re-exports now come from @seamless-auth/core, folded into the existing SeamlessUser re-export.
• src/createServer.ts: SeamlessAuthMessagingOptions imported from core.
• src/internal/deliverAuthMessage.ts: AuthDeliveryInstruction, EmailMessage, SeamlessAuthMessagingOptions, and SmsMessage imported from core.

No public surface change

Verified rather than assumed. Clean-built the emitted .d.ts on main and on this branch and diffed them. The only differences are the module specifier the types are re-exported from; the set of exported names is unchanged:

< export type { AuthMessageOverrides, ..., SmsTransport, } from "./messaging";
< export type { SeamlessUser } from "@seamless-auth/core";
---
> export type { AuthMessageOverrides, ..., SeamlessUser, ..., SmsTransport, } from "@seamless-auth/core";

dist/messaging.d.ts is gone, but it was never reachable by adopters: the package declares only a root . export, no subpaths. @seamless-auth/core is already a real dependencies entry, so the types resolve for consumers.

The types the adapter and core share are now one declaration rather than two structurally identical ones.

Not in scope

The issue's "Related" note suggests core could take the pure data shapes from @seamless-auth/types instead of declaring them. That overlaps #120 and is left for a separate PR. Worth knowing before that one is picked up: the role module is not in the published @seamless-auth/types@0.1.3, so #120 is blocked on a release from that repo.

Checks

pnpm build clean. pnpm test passes: 43 suites, 205 tests. Patch changeset added for @seamless-auth/express.