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/TypingAutocapitalization.swift

@@ -0,0 +1,69 @@
+// TypingAutocapitalization.swift
+// OSGKeyboard · Shared
+//
+// Decides when the English letter page should arm Shift once for
+// automatic capitalization (mirrors UITextAutocapitalizationType).
+
+import Foundation
+
+public enum TypingAutocapitalizationMode: String, Sendable, Equatable {
+    case none
+    case words
+    case sentences
+    case allCharacters
+}
+
+public enum TypingAutocapitalization: Sendable {
+    /// Whether Shift should be armed for the next Latin letter.
+    public static func shouldCapitalize(
+        precedingText: String?,
+        mode: TypingAutocapitalizationMode
+    ) -> Bool {
+        switch mode {
+        case .none:
+            return false
+        case .allCharacters:
+            return true
+        case .words:
+            return needsWordCapitalization(precedingText)
+        case .sentences:
+            return needsSentenceCapitalization(precedingText)
+        }
+    }
+
+    // MARK: - Private
+
+    private static func needsWordCapitalization(_ preceding: String?) -> Bool {
+        guard let preceding, !preceding.isEmpty else { return true }
+        guard let last = preceding.last else { return true }
+        return last.isWhitespace || last.isNewline
+    }
+
+    private static func needsSentenceCapitalization(_ preceding: String?) -> Bool {
+        guard let preceding, !preceding.isEmpty else { return true }
+
+        // Walk backward past trailing whitespace / newlines; capitalize when
+        // the field is empty or the previous visible character ends a sentence.
+        var index = preceding.endIndex
+        var sawContent = false
+        while index > preceding.startIndex {
+            index = preceding.index(before: index)
+            let character = preceding[index]
+            if character.isWhitespace || character.isNewline {
+                continue
+            }
+            sawContent = true
+            return isSentenceTerminator(character)
+        }
+        return !sawContent
+    }
+
+    private static func isSentenceTerminator(_ character: Character) -> Bool {
+        switch character {
+        case ".", "!", "?", "…", "。", "！", "？":
+            return true
+        default:
+            return false
+        }
+    }
+}