feat(keyboard): add English QuickType bar and system lexicon

Show verbatim/correction/completion slots, mmap a 40k-word list, and
use UITextChecker plus supplementary lexicon for conservative autocorrect.

OSGKeyboardUITests/EnglishKeyboardDeviceUITests.swift

@@ -0,0 +1,43 @@
+// EnglishKeyboardDeviceUITests.swift
+// OSGKeyboardUITests
+//
+// Physical-device pass: Notes-like host + the real keyboard extension.
+// Skips if OSGKeyboard is not enabled as the current keyboard.
+
+import XCTest
+
+final class EnglishKeyboardDeviceUITests: XCTestCase {
+    func testOSGKeyboardAppearsOnNotesHost() throws {
+        let app = XCUIApplication()
+        app.launchArguments = [
+            "--whats-new-host",
+            "--whats-new-lang=en",
+            "--whats-new-scenario=edit"
+        ]
+        app.launch()
+
+        let textView = app.textViews["notes.host.textView"]
+        XCTAssertTrue(
+            textView.waitForExistence(timeout: 12),
+            "Notes host text view should appear"
+        )
+        if !textView.exists {
+            return
+        }
+        textView.tap()
+
+        let keyboard = XCUIApplication(bundleIdentifier: "com.osgkeyboard.ios.keyboard")
+        let appeared = keyboard.wait(for: .runningForeground, timeout: 8)
+            || keyboard.windows.firstMatch.waitForExistence(timeout: 8)
+        if !appeared {
+            throw XCTSkip(
+                "OSGKeyboard extension is not the active keyboard on this device. Enable it in Settings ▸ Keyboard, then re-run."
+            )
+        }
+
+        XCTAssertTrue(
+            keyboard.windows.firstMatch.exists,
+            "OSGKeyboard extension window should be on screen"
+        )
+    }
+}