feat(typing): add English autocomplete and Chinese candidate expand panel

Offline English lexicon suggestions with autocapitalization, plus a same-height Chinese more-candidates grid over the key area.

OSGKeyboardShared/Typing/TypingOutput.swift

@@ -0,0 +1,37 @@
+// TypingOutput.swift
+// OSGKeyboard · Shared
+//
+// Unified mutation the typing UI applies to UITextDocumentProxy.
+// English autocorrect / completion need multi-delete + insert; Chinese
+// mostly inserts or issues a single backspace sentinel.
+
+import Foundation
+
+/// Text mutation produced by one typing action.
+public struct TypingOutput: Equatable, Sendable {
+    /// How many `deleteBackward` calls to issue before inserting.
+    public var deleteCount: Int
+    /// Text to insert after deletions (may be empty).
+    public var text: String
+
+    public init(deleteCount: Int = 0, text: String = "") {
+        self.deleteCount = deleteCount
+        self.text = text
+    }
+
+    public static let none = TypingOutput()
+
+    public static func insert(_ text: String) -> TypingOutput {
+        TypingOutput(deleteCount: 0, text: text)
+    }
+
+    public static let backspace = TypingOutput(deleteCount: 1, text: "")
+
+    public static func replace(deleteCount: Int, with text: String) -> TypingOutput {
+        TypingOutput(deleteCount: deleteCount, text: text)
+    }
+
+    public var isEmpty: Bool {
+        deleteCount == 0 && text.isEmpty
+    }
+}