feat(tui): add prompt history navigation with Up/Down arrows

Browse previously submitted prompts using Up/Down arrow keys, similar to
shell history and Claude Code's prompt history feature.

- Up arrow when editor is empty: browse to older prompts
- Down arrow when browsing: return to newer prompts or clear editor
- Cursor movement within multi-line history entries supported
- History is session-scoped, stores up to 100 entries
- Consecutive duplicates are not added to history

Includes 15 new tests for history navigation behavior.

packages/coding-agent/src/tui/tui-renderer.ts

@@ -516,6 +516,9 @@ export class TuiRenderer {
 				// Update pending messages display
 				this.updatePendingMessagesDisplay();
 
+				// Add to history for up/down arrow navigation
+				this.editor.addToHistory(text);
+
 				// Clear editor
 				this.editor.setText("");
 				this.ui.requestRender();
@@ -526,6 +529,9 @@ export class TuiRenderer {
 			if (this.onInputCallback) {
 				this.onInputCallback(text);
 			}
+
+			// Add to history for up/down arrow navigation
+			this.editor.addToHistory(text);
 		};
 
 		// Start the UI