feat(desktop): forward renderer console + crash events to main stderr in dev

When the renderer crashes hard enough to leave a white window (React
boundary unrecoverable, syntax error during initial mount, preload
script throw), DevTools can't be opened and the only signal in the
`make dev` terminal is the daemon-manager 5s polling complaint
("Render frame was disposed before WebFrameMain could be accessed").
That's a downstream symptom — the actual JS error is unreachable, so
the user has no path to diagnose without restarting the renderer
(which loses the failure mode entirely).

Add four webContents listeners on the main BrowserWindow, gated by
`is.dev` so packaged builds keep their stderr clean:

- `console-message`: forwards every renderer `console.*` to main's
  stderr with file:line. React error boundaries, `window.onerror`, and
  unhandled-rejection handlers all surface here.
- `render-process-gone`: serialises the GoneDetails (`crashed` / `oom`
  / `killed` / `launch-failed`) so the user sees *why* the renderer
  died, not just that it did.
- `did-fail-load`: catches loadURL/loadFile failures. Skip
  `errorCode === -3 (ABORTED)` because that's the normal HMR-induced
  navigation abort.
- `preload-error`: the one error class DevTools can never show, because
  preload runs before the window owns a console. Without this listener
  preload throws are invisible.

All output is prefixed with `[renderer <tag>]` so it's easy to grep
distinct from main's own logs.

No behavioural change in production: the entire block is inside an
`is.dev` guard. Packaged builds keep their existing stderr.

apps/desktop/src/main/index.ts

@@ -200,6 +200,57 @@ function createWindow(): void {
     }
   });
 
+  // Dev-mode renderer diagnostics. When the renderer crashes hard enough
+  // that DevTools can't be opened (white screen with no clickable surface),
+  // the only way to recover the actual JS error is to forward it from the
+  // main process to the terminal running `make dev`. Without these, the
+  // user sees only the daemon-manager polling noise (`Render frame was
+  // disposed before WebFrameMain could be accessed`) which is a downstream
+  // symptom, not the cause.
+  //
+  // Gated by `is.dev` to keep production stderr clean — packaged builds
+  // don't have a terminal anyway, and we ship to crash-reporting separately.
+  if (is.dev) {
+    const log = (tag: string, ...args: unknown[]) =>
+      process.stderr.write(`[renderer ${tag}] ${args.map(String).join(" ")}\n`);
+
+    // Forward every renderer-side console.* call. The detail object also
+    // carries source URL + line — included so a thrown stack trace from
+    // window.onerror is traceable back to a file.
+    mainWindow.webContents.on("console-message", (details) => {
+      const { level, message, sourceId, lineNumber } = details;
+      log(level, `${message} (${sourceId}:${lineNumber})`);
+    });
+
+    // Fires when the renderer process dies for any reason (OOM, crash,
+    // killed). `details.reason` is the discriminator: "crashed", "oom",
+    // "killed", "abnormal-exit", "launch-failed", etc.
+    mainWindow.webContents.on("render-process-gone", (_event, details) => {
+      log("process-gone", JSON.stringify(details));
+    });
+
+    // Fires when loadURL / loadFile can't reach its target (dev server
+    // not up yet, network blip, file missing). errorCode is a Chromium
+    // net error number; -3 = ABORTED is normal during HMR and skipped.
+    mainWindow.webContents.on(
+      "did-fail-load",
+      (_event, errorCode, errorDescription, validatedURL, isMainFrame) => {
+        if (errorCode === -3) return;
+        log(
+          "did-fail-load",
+          `code=${errorCode} desc=${errorDescription} url=${validatedURL} mainFrame=${isMainFrame}`,
+        );
+      },
+    );
+
+    // Fires when the preload script throws before the renderer can boot.
+    // This is the one error class that NEVER reaches DevTools (preload
+    // runs before any window) — without this listener it's invisible.
+    mainWindow.webContents.on("preload-error", (_event, preloadPath, error) => {
+      log("preload-error", `path=${preloadPath} err=${error?.stack ?? error}`);
+    });
+  }
+
   installContextMenu(mainWindow.webContents);
 
   if (is.dev && process.env["ELECTRON_RENDERER_URL"]) {