feat(testing): smoke-test script + VITE_FORCE_BOOT_STALL gate

- App.tsx and main.tsx ErrorBoundary gate rendererReady() on
  VITE_FORCE_BOOT_STALL build env var. When set, the ping is suppressed
  so the main-process boot timer fires (exercising the renderer-stalled
  recovery path without hand-editing source).
- vite-env.d.ts declares the env var type so TS doesn't complain.
- scripts/smoke-recovery.sh automates scenarios 2 (bad URL → load-failed)
  and 4 (forced stall → renderer-stalled), grepping stderr for the
  [recovery] entered: ... lines added by the prior commit. Backs up and
  restores the user's instance-url.json. Manual scenarios documented in
  the script header.

packages/web/src/App.tsx

@@ -34,7 +34,12 @@ export function App() {
   // first commit; main owns "armed once" gating so duplicate calls (e.g.
   // ErrorBoundary path) are idempotent. Semantic: "renderer survived
   // render," NOT "data loaded." A spinner on screen counts as boot success.
+  //
+  // Gated on VITE_FORCE_BOOT_STALL so the smoke-test harness can build a
+  // variant that intentionally never pings, exercising the renderer-stalled
+  // recovery path without hand-editing source. Set 'true' / '1' to force stall.
   useEffect(() => {
+    if (import.meta.env.VITE_FORCE_BOOT_STALL) return;
     if (typeof window.backspace?.rendererReady === 'function') {
       window.backspace.rendererReady();
     }

packages/web/src/main.tsx

@@ -23,6 +23,9 @@ class ErrorBoundary extends React.Component<
     // Renderer is alive enough to show the fallback UI — disarm the boot timer.
     // Without this, the timer fires 20s after a caught render error and
     // overrides the in-app error UI with native recovery, which is wrong.
+    // Gated on VITE_FORCE_BOOT_STALL so the smoke harness can suppress both
+    // ping paths simultaneously when testing the renderer-stalled recovery path.
+    if (import.meta.env.VITE_FORCE_BOOT_STALL) return;
     if (typeof window.backspace?.rendererReady === 'function') {
       window.backspace.rendererReady();
     }

packages/web/src/vite-env.d.ts

@@ -1,5 +1,12 @@
 /// <reference types="vite/client" />
 
+interface ImportMetaEnv {
+  readonly VITE_FORCE_BOOT_STALL?: string;
+}
+interface ImportMeta {
+  readonly env: ImportMetaEnv;
+}
+
 declare module '@sapphi-red/web-noise-suppressor/rnnoiseWorklet.js?url' {
   const url: string;
   export default url;