perf: faster plugin updates, half-size first bundle, images from the chat attach on Windows

- Chat view: an attached image's path is pasted on its own after the text
  (promptForPane). claude turns a paste that is only an image path into
  [Image #n], but left a Windows path inside a paste of text as a plain path.
  Other files and @-mentions stay in the text as before.
- Plugin bootstrap: depsHash covers only what npm installs (no release
  version), so a version bump no longer reinstalls runtime deps; the client's
  installed tree is kept while its manifests are unchanged (no npm ci per
  update); the user-side build runs vite only (tsc -b cost ~25 s / ~900 MB);
  clientBuild is recorded only after a build that did not fail, so a failed
  one is retried; npm output goes to runtime/npm-install.log.
- Server: a port held by another program ends with a clear message and exit 1
  instead of an uncaught 'error' stack trace.
- Client: the onboarding wizard is lazy and rendered only before onboarding;
  usePrefersReducedMotion moved to hooks/ so PetSettings no longer pulls the
  Sagi chat/pane stack into the entry chunk (884 KB -> 431 KB, gzip 268 -> 133 KB).

client/src/components/Layout.tsx

@@ -76,7 +76,7 @@
  *
  * ----------------------------------------------------------------------------- */
 
-import { useState, useCallback, useEffect, useSyncExternalStore } from "react";
+import { lazy, Suspense, useState, useCallback, useEffect, useSyncExternalStore } from "react";
 import { Outlet, useLocation } from "react-router-dom";
 import { Menu } from "lucide-react";
 import { useTranslation } from "react-i18next";
@@ -85,9 +85,15 @@ import { UpdateNotifier } from "./UpdateNotifier";
 import { InterruptedSessionsPrompt } from "./lanes/InterruptedSessionsPrompt";
 import { SagiMount } from "./Sagi/SagiMount";
 import { StatusBar } from "./StatusBar";
-import { OnboardingWizard } from "./onboarding/OnboardingWizard";
+import { useOnboarding } from "../lib/userPrefs";
 import { OnboardingTour } from "./onboarding/OnboardingTour";
 
+// Loaded only for an account that has not finished onboarding: the wizard
+// carries the appearance, pet and notification settings screens.
+const OnboardingWizard = lazy(() =>
+  import("./onboarding/OnboardingWizard").then((m) => ({ default: m.OnboardingWizard }))
+);
+
 const WIDTH_KEY = "agenthub.sidebar.width";
 /** The default width, and the narrowest the edge drags to. */
 export const SIDEBAR_MIN = 240;
@@ -136,6 +142,7 @@ export function Layout({ wsConnected }: LayoutProps) {
   const { t } = useTranslation("nav");
   const [collapsed, setCollapsed] = useState(loadCollapsed);
   const [connectionOpen, setConnectionOpen] = useState(false);
+  const onboarding = useOnboarding();
   const [updateAvailable, setUpdateAvailable] = useState(false);
   const drawer = useMedia(DRAWER_QUERY);
   const [drawerOpen, setDrawerOpen] = useState(false);
@@ -177,7 +184,11 @@ export function Layout({ wsConnected }: LayoutProps) {
       <UpdateNotifier />
       <InterruptedSessionsPrompt />
       <SagiMount />
-      <OnboardingWizard />
+      {onboarding.loaded && !onboarding.onboardedAt && (
+        <Suspense fallback={null}>
+          <OnboardingWizard />
+        </Suspense>
+      )}
       <OnboardingTour />
       {drawer && drawerOpen && (
         <div