Add synchronized output support (DEC mode 2026)

Implement synchronized output mode (CSI ? 2026 h/l) which allows
applications to batch terminal updates and render them atomically,
preventing screen tearing during rapid output.

Features:
- BSU (CSI ? 2026 h) pauses rendering, buffering row updates
- ESU (CSI ? 2026 l) flushes buffer and renders atomically
- Configurable timeout via synchronizedOutputTimeout option (default 5s)
- Exposed via terminal.modes.synchronizedOutputMode

Closes #3375

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

src/common/InputHandler.ts

@@ -1969,6 +1969,9 @@ export class InputHandler extends Disposable implements IInputHandler {
         case 2004: // bracketed paste mode (https://cirw.in/blog/bracketed-paste)
           this._coreService.decPrivateModes.bracketedPasteMode = true;
           break;
+        case 2026: // synchronized output (https://gist.github.com/christianparpart/d8a62cc1ab659194337d73e399004036)
+          this._coreService.decPrivateModes.synchronizedOutput = true;
+          break;
       }
     }
     return true;
@@ -2197,6 +2200,11 @@ export class InputHandler extends Disposable implements IInputHandler {
         case 2004: // bracketed paste mode (https://cirw.in/blog/bracketed-paste)
           this._coreService.decPrivateModes.bracketedPasteMode = false;
           break;
+        case 2026: // synchronized output (https://gist.github.com/christianparpart/d8a62cc1ab659194337d73e399004036)
+          this._coreService.decPrivateModes.synchronizedOutput = false;
+          // Trigger a full refresh now that the synchronized output block has ended
+          this._onRequestRefreshRows.fire(undefined);
+          break;
       }
     }
     return true;