feat(keyboard): improve typing, voice flow, and polish reliability

Reduce extension memory pressure and delivery races while adding richer candidates, tactile feedback, and safer two-level creative polishing.

OSGKeyboardHostSupport/Models/AudioBufferSnapshot+AVFoundation.swift

@@ -0,0 +1,25 @@
+// AudioBufferSnapshot+AVFoundation.swift
+// OSGKeyboard · HostSupport
+//
+// AVAudioPCMBuffer → AudioBufferSnapshot copy helper. Kept out of Shared so
+// the keyboard extension does not link AVFoundation for this type alone.
+
+import AVFoundation
+import Foundation
+#if canImport(OSGKeyboardShared)
+import OSGKeyboardShared
+#endif
+
+extension AudioBufferSnapshot {
+    /// Construct from an `AVAudioPCMBuffer` by copying out the channel data.
+    public init(buffer: AVAudioPCMBuffer) {
+        guard let channelData = buffer.floatChannelData else {
+            self.init(samples: [], sampleRate: buffer.format.sampleRate)
+            return
+        }
+        let n = Int(buffer.frameLength)
+        var copy = [Float](repeating: 0, count: n)
+        memcpy(&copy, channelData[0], n * MemoryLayout<Float>.size)
+        self.init(samples: copy, sampleRate: buffer.format.sampleRate)
+    }
+}