fix(sdk): drop unused svelte and vue peer dependencies (#2727)

`@langchain/langgraph-sdk` declared `svelte` and `vue` as optional peer
dependencies, but the adapters for both moved to `@langchain/svelte` and
`@langchain/vue` and the core SDK never imports either one.

Socket (and similar scanners) treat optional peers as part of the
package graph, so the SDK was showing two high alerts for obfuscated
code in `clsx` and `entities` — transitive deps of Svelte and Vue that
the SDK never loads. Removing the peers drops the reported dependency
count from 9 to 7 and clears both alerts.

React is unchanged: `./react` and `./react-ui` still ship from this
package, so it stays an optional peer.