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/settings/PetSettings.tsx

@@ -28,7 +28,7 @@ import { SettingsRow, SettingsSwitchRow } from "./SettingsRow";
 import { SagiAvatar } from "../Sagi/SagiAvatar";
 import { PetSprite } from "../Sagi/PetSprite";
 import { PET_SIZE, sagiPrefs } from "../Sagi/prefs";
-import { usePrefersReducedMotion } from "../Sagi/Sagi";
+import { usePrefersReducedMotion } from "../../hooks/usePrefersReducedMotion";
 import { confirmDialog } from "../../lib/confirm";
 import { toast } from "../../lib/toast";
 import { usePets, useWornPet } from "../Sagi/usePets";