fix(chat): drop the now-unused @langchain/core peer dependency

Widening messageContent() to { content: unknown } removed the last
LangChain import from the published package, so @nx/dependency-checks
fails the declared peer. It stays a peer of @threadplane/langgraph,
which is why the install command still lists it.

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

Author: blove

apps/website/content/docs/chat/getting-started/installation.mdx

@@ -58,15 +58,14 @@ every required peer for you, so the install command above is enough.
 | `@threadplane/render` | `0.0.66` | yes |
 | `@threadplane/a2ui` | `0.0.66` | yes |
 | `@json-render/core` | `^0.16.0` | yes |
-| `@langchain/core` | `^1.1.33` | yes |
 | `rxjs` | `~7.8.0` | yes |
 | `marked` | `^15.0.0 \|\| ^16.0.0` | yes |
 | `zod` | `^3.25.0` | yes |
 | `katex` | `^0.16.0 \|\| ^0.17.0` | optional |
 
 Installing `@threadplane/chat` therefore also brings in `@threadplane/telemetry`,
-`@threadplane/render`, `@threadplane/a2ui`, `@json-render/core`,
-`@langchain/core`, `rxjs`, `marked`, and `zod`.
+`@threadplane/render`, `@threadplane/a2ui`, `@json-render/core`, `rxjs`,
+`marked`, and `zod`.
 </Callout>
 
 ## 2. Configure the runtime

libs/chat/CHANGELOG.md

@@ -4,6 +4,9 @@
 
 ### Removed
 
+- **`@langchain/core` is no longer a peer dependency.** `messageContent()` now takes
+  any `{ content: unknown }`, so nothing in the published package imports LangChain.
+  Keep installing it for `@threadplane/langgraph`, which still requires it.
 - **`provideChat()`, `ChatConfig`, and `CHAT_CONFIG` are gone.** No component in the library ever injected the token, so calling `provideChat({})` configured nothing: `renderRegistry`, `avatarLabel`, and `assistantName` were values only your own wrappers could read back. Delete the call and the import; `provideAgent()` from your runtime adapter is the only provider the chat components require, and everything they render is driven by component inputs. If you were reading `CHAT_CONFIG` from your own components, define your own injection token for those values.
 
 ### Fixed

libs/chat/package.json

@@ -27,7 +27,6 @@
     "@threadplane/render": "0.0.66",
     "@threadplane/a2ui": "0.0.66",
     "@json-render/core": "^0.16.0",
-    "@langchain/core": "^1.1.33",
     "rxjs": "~7.8.0",
     "marked": "^15.0.0 || ^16.0.0",
     "katex": "^0.16.0 || ^0.17.0"