fix(coding-agent): expand paste markers in Ctrl+Q follow-ups

InputController.handleFollowUp read raw editor text via getText(),
bypassing the paste-store expansion the Enter path applies through
Editor.getExpandedText(). A large paste collapsed into a [Paste #N, +X
lines] marker was therefore sent verbatim to the model when queued with
Ctrl+Q / Ctrl+Enter, silently dropping the pasted content.

Switch the follow-up path to getExpandedText() so queued submissions
match the Enter path. Image markers are untouched; pendingImages
forwarding is unchanged.

Updated existing input-controller stubs (skill-queue, followup-image,
keybindings) to implement getExpandedText, matching the production
CustomEditor surface.

Fixes #3737

packages/coding-agent/test/input-controller-keybindings.test.ts

@@ -26,6 +26,7 @@ type FakeEditor = {
 	onSubmit?: (text: string) => Promise<void>;
 	setText(text: string): void;
 	getText(): string;
+	getExpandedText(): string;
 	addToHistory(text: string): void;
 	setActionKeys(action: string, keys: string[]): void;
 	setCustomKeyHandler(key: string, handler: () => void): void;
@@ -105,6 +106,9 @@ async function createContext() {
 		getText() {
 			return editorText;
 		},
+		getExpandedText() {
+			return editorText;
+		},
 		addToHistory: vi.fn(),
 		pasteText(text: string) {
 			editorText += text;