Build the fork with Xcode 27

Xcode 27 ships Swift 6.4, which rejects two things 26.09.1 still contains. The
upstream fix for the app itself is cherry-picked as the commit before this one;
these two are what it does not cover.

Compound's colour overrides now take a KeyPath & Sendable, so the HealthChat
brand arrays have to carry the same constraint.

NotificationContentBuilder is main-actor isolated, so its test suite has to
build the type from an async init. The lines match upstream's own fix, which
only exists inside the larger AccountProvider change (#6103) and so cannot be
cherry-picked on its own.

ElementX/Sources/AppHooks/HealthChat/HealthChatCompoundHook.swift

@@ -30,7 +30,7 @@ struct HealthChatCompoundHook: CompoundHookProtocol {
             \.borderInteractivePrimary,
             \.textBadgeAccent
         ]
-        let solidUIColorTokens: [KeyPath<CompoundUIColorTokens, UIColor>] = [
+        let solidUIColorTokens: [KeyPath<CompoundUIColorTokens, UIColor> & Sendable] = [
             \.bgActionPrimaryRest,
             \.bgAccentRest,
             \.iconAccentPrimary,
@@ -69,7 +69,7 @@ struct HealthChatCompoundHook: CompoundHookProtocol {
             \.bgBadgeAccent,
             \.borderAccentSubtle
         ]
-        let tintUIColorTokens: [KeyPath<CompoundUIColorTokens, UIColor>] = [
+        let tintUIColorTokens: [KeyPath<CompoundUIColorTokens, UIColor> & Sendable] = [
             \.bgAccentSelected,
             \.bgBadgeAccent,
             \.borderAccentSubtle