Migrate Demo to ExyteChat 3.x and unblock the build on Xcode 27

CLAUDE.md

@@ -19,3 +19,34 @@ that still calls a removed/renamed API. The goal is for Demo to stay complete
 and up to date with the package, not silently lag behind. Only skip this
 build when the change clearly cannot affect Demo (docs, CI config, tests-only
 changes, etc.).
+
+## Foundation types that don't exist on Linux
+
+CI builds and tests this package on Linux (Swift 5.10, 6.0, 6.3) in addition
+to Apple platforms. Several `Foundation` types you'd normally reach for
+without a second thought — `HTTPURLResponse`, `URLSession.*` nested types
+(e.g. `ResponseDisposition`), `URLRequest` in some contexts, etc. — live in
+the separate `FoundationNetworking` module on Linux, not in `Foundation`
+itself. Code that uses them compiles fine on macOS and fails on Linux CI
+only, with an error like `'HTTPURLResponse' is unavailable: This type has
+moved to the FoundationNetworking module.`
+
+Whenever a new file (source *or* test) references one of these types, guard
+the import the way existing files already do:
+
+```swift
+import Foundation
+#if canImport(FoundationNetworking)
+import FoundationNetworking
+#endif
+```
+
+`swift build` / `swift test` passing locally on macOS does not confirm this —
+the failure only shows up on Linux. If you can't run the Linux job yourself,
+at least double-check new files against this pattern before considering the
+change done.
+
+## Wait for explicit instructions to push
+
+CI takes several minutes to run, so commit locally as you go but don't run
+`git push` unless the user explicitly asks for it at that point.

Demo/DemoChat/Package.swift

@@ -14,8 +14,13 @@ let package = Package(
     ],
     dependencies: [
         .package(name: "OpenAI", path: "../.."),
-        .package(url: "https://github.com/exyte/Chat.git", from: "2.5.7"),
-        .package(url: "https://github.com/modelcontextprotocol/swift-sdk.git", from: "0.9.0")
+        .package(url: "https://github.com/exyte/Chat.git", from: "3.3.3"),
+        .package(url: "https://github.com/modelcontextprotocol/swift-sdk.git", from: "0.9.0"),
+        // Pinned explicitly: MediaPicker 3.4.x calls PopupParameters.displayMode(_:), which
+        // AnchoredPopup only added in 1.2.0. MediaPicker's own manifest still declares
+        // `from: "1.1.3"`, so without this override SwiftPM's version resolution can pick
+        // 1.1.3 and fail to build.
+        .package(url: "https://github.com/exyte/AnchoredPopup.git", from: "1.2.2")
     ],
     targets: [
         .target(