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).

SETUP.md

@@ -401,18 +401,16 @@ This was a known timezone bug (fixed in current version). If you are still seein
 
 ### Port 4820 already in use
 
+When another program holds the port, the server stops with
+`Port 4820 is already in use by another program…` (a running AgentHub there is
+detected and simply reused). Pick another port:
+
 ```bash
-DASHBOARD_PORT=4821 npm run dev
+DASHBOARD_PORT=4821 npm start      # or: DASHBOARD_PORT=4821 npm run dev
 ```
 
-Then update the Vite proxy in `client/vite.config.ts`:
-
-```ts
-proxy: {
-  "/api": "http://localhost:4821",
-  "/ws":  { target: "ws://localhost:4821", ws: true }
-}
-```
+The Vite dev proxy and the Claude Code hooks follow the port on their own
+(`client/vite.config.ts` reads `DASHBOARD_PORT`; the server publishes the port it bound).
 
 And make sure Claude Code posts hooks to the new port: