feat(keyboard): unify assistant voice and AI workflows

Merge dictation and AI controls into one assistant surface, preserve safe insertion and clipboard actions, and align settings and tests with the new flow.

OSGKeyboardShared/Models/AISessionState.swift

@@ -190,6 +190,18 @@ public struct AISessionState: Equatable, Sendable {
         phase = .sent
     }
 
+    /// Drops a result retained because the insertion target changed.
+    /// The conversation remains active so the user can immediately ask again.
+    public mutating func discardReadyAnswer() {
+        guard phase == .ready else { return }
+        answer = nil
+        activeUtteranceID = nil
+        draftAnswerText = nil
+        transcript = ""
+        errorMessage = nil
+        phase = .idle
+    }
+
     public mutating func cancelCurrentWork() {
         guard isBusy else { return }
         activeUtteranceID = nil