refactor(flow): remove Live Activity and keep-alive mode picker

Keep voice sessions on silent low-profile PiP only, and fix custom polish style editor presentation via sheet(item:).

OSGKeyboardShared/Models/ProviderConfig.swift

@@ -259,22 +259,7 @@ public final class ProviderConfig: ObservableObject, @unchecked Sendable {
         }
     }
 
-    /// PiP vs Live Activity keep-alive (mutually exclusive).
-    @Published public var flowKeepAliveMode: FlowKeepAliveMode {
-        didSet {
-            guard !isApplyingConfiguration, flowKeepAliveMode != configuration.flowKeepAliveMode else { return }
-            configuration.flowKeepAliveMode = flowKeepAliveMode
-            if flowKeepAliveMode == .pictureInPicture {
-                configuration.flowSkipAppSwitch = true
-                if flowSkipAppSwitch != true {
-                    flowSkipAppSwitch = true
-                }
-            }
-            persistConfiguration()
-        }
-    }
-
-    /// Idle window before an active Flow session expires; Live Activity mode only.
+    /// Retained for storage compatibility; persistent PiP sessions do not expire from inactivity.
     @Published public var flowInactivityDuration: FlowInactivityDuration {
         didSet {
             guard !isApplyingConfiguration,
@@ -406,7 +391,6 @@ public final class ProviderConfig: ObservableObject, @unchecked Sendable {
         polishIntensity = configuration.polishIntensity
         llmThinkingEnabled = configuration.llmThinkingEnabled
         flowSkipAppSwitch = configuration.flowSkipAppSwitch
-        flowKeepAliveMode = configuration.flowKeepAliveMode
         flowInactivityDuration = configuration.flowInactivityDuration
         localASRCustomLanguageModelEnabled = configuration.localASRCustomLanguageModelEnabled
         isSyncingProviderAPIKey = true
@@ -498,7 +482,6 @@ public final class ProviderConfig: ObservableObject, @unchecked Sendable {
         polishIntensity = fresh.polishIntensity
         llmThinkingEnabled = fresh.llmThinkingEnabled
         flowSkipAppSwitch = fresh.flowSkipAppSwitch
-        flowKeepAliveMode = fresh.flowKeepAliveMode
         flowInactivityDuration = fresh.flowInactivityDuration
         localASRCustomLanguageModelEnabled = fresh.localASRCustomLanguageModelEnabled
         isSyncingProviderAPIKey = true