feat: test parity final push — 64 new tests, BSU/ESU, clear() API

Closes remaining test gaps between vue-tui and Ink:

Features:
- Add synchronized output (BSU/ESU) via DEC private mode 2026
- Add clear() API to TuiApp for erasing rendered output

Bug fixes:
- Cancel scheduler trailing timer on teardown (prevents stale commits)
- Guard teardown writes against ended/destroyed streams
- Reorder teardown to cancel timer before final commit

Tests (64 new, 2 skipped for known feature gaps):
- 7 BSU/ESU shouldSynchronize tests
- 5 borderBackgroundColor tests
- 13 component edge cases (empty text, number child, OSC hyperlink
  wrap-width, bare-text-in-Box validation, transform multi-line,
  leading whitespace, link escape closing)
- 13 text-width/CJK tests (alignment, truncation, overlay edge cases)
- 4 throttle + unmount edge cases
- 10 waitUntilRenderFlush write-callback-level tests + 1 clear() test
- 3 exit re-entrance tests
- 5 PTY #450 regression tests + 4 inline #450 tests

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

packages/runtime-tests/vitest.pty.config.ts

@@ -1,8 +1,10 @@
 import { defineConfig } from "vite-plus";
+import vueJsx from "@vitejs/plugin-vue-jsx";
 
 export default defineConfig({
+  plugins: [vueJsx()],
   test: {
-    include: ["integration/pty/**/*.test.ts"],
+    include: ["integration/pty/**/*.test.{ts,tsx}"],
     fileParallelism: false,
     testTimeout: 15000,
     env: { FORCE_COLOR: "3" },