Architecture refactor: docs + 5 pilot implementations + error boundary

This is the structural plan promised in the previous session, with concrete
pilots for all five proposals + the bonus error-boundary work.

== docs/ARCHITECTURE.md (new, ~370 lines)

Living document describing:
- where the project stands today (event-bus pattern friction with React 19,
  god-hooks, oversized files);
- the five proposed structural improvements with the why/how/status of each;
- what's already in place across this branch;
- recommended order for the next refactor PRs.

This is the deliverable the rest of this commit references.

== Proposal #3 + #4 pilots: src/features/doorbell/ (new)

Concrete feature-folder migration on the doorbell widget (chosen because
it's small enough to migrate end-to-end in one commit).

  src/features/doorbell/
    index.ts                    public API
    views/DoorbellWidgetView.tsx
    hooks/useDoorbellState.ts   reduces 3 events into a users array (data only)
    hooks/useDoorbellActions.ts answer(name, flag) (imperative actions only)

The split (data vs actions) is the pattern proposal #4 wants applied to
useCatalog/useChat/useWiredTools later. The original useDoorbellWidget had
both concerns + a buggy `useEffect(() => setIsVisible(!!users.length), [users])`
derive-state-in-effect. The new view computes visibility in render.

Compat shims kept so existing imports keep working:
- src/components/room/widgets/doorbell/DoorbellWidgetView.tsx -> 1-line re-export
- src/hooks/rooms/widgets/useDoorbellWidget.ts -> deprecated wrapper around
  the two new hooks, returning the same { users, answer } shape.

== Proposal #2 prototype: src/api/nitro-query/ (new)

Adapter outline for wrapping composer/parser request-response pairs in
TanStack Query. Not yet enabled because @tanstack/react-query is not in
package.json. The file documents the activation steps:

  yarn add @tanstack/react-query @tanstack/react-query-devtools
  + mount QueryClientProvider in src/index.tsx

awaitNitroResponse() throws with a helpful pointer to the doc section if
called before activation, so accidental adoption fails loudly.

== Proposal #5 skeleton: src/state/createNitroStore.ts (new)

Same pattern: skeleton + activation instructions. Not yet enabled because
zustand is not in package.json.

  yarn add zustand
  + replace the throw with `import { create } from 'zustand'; export const createNitroStore = create;`

The doc inside the file shows the recommended slice shape and points to
the suggested first migration target (the let isCreatingRoom singleton in
NavigatorRoomCreatorView).

== Bonus: WidgetErrorBoundary

src/common/error-boundary/WidgetErrorBoundary.tsx wraps react-error-boundary
with a sensible default (silent fallback, NitroLogger.error). Re-exported
from src/common/index.ts.

Applied as the umbrella around RoomWidgetsView's children — a widget
crash in a room (e.g. malformed pet data) now degrades gracefully
instead of unmounting the whole UI.

== Verification

- yarn eslint on all new + modified files: 0 errors / 0 warnings introduced.
  RoomWidgetsView still has its 1 pre-existing FC<{}> error (1 before, 1 after).
- yarn tsc on all new files: clean (only project-wide pre-existing
  TS2307 about @nitrots/nitro-renderer not installed locally remains).
- No regressions: existing imports of DoorbellWidgetView and
  useDoorbellWidget keep resolving via the compat shims.

== What's NOT in this commit (intentionally)

- Mass adoption of the new patterns elsewhere — left as follow-up PRs in
  the order documented in ARCHITECTURE.md "How to pick the next refactor PR".
- Installation of @tanstack/react-query / zustand — explicit team decision,
  not the LLM's to make.
- Test infrastructure (Vitest setup) — listed as the #1 missing piece in
  the doc, but a separate PR.

https://claude.ai/code/session_01GrR87LAqnAEyKG2ZbmQt5Q

src/components/room/widgets/RoomWidgetsView.tsx

@@ -1,6 +1,7 @@
 import { GetRoomEngine, RoomEngineObjectEvent, RoomEngineRoomAdEvent, RoomEngineTriggerWidgetEvent, RoomEngineUseProductEvent, RoomId, RoomSessionErrorMessageEvent, RoomZoomEvent } from '@nitrots/nitro-renderer';
 import { FC } from 'react';
 import { DispatchUiEvent, LocalizeText, NotificationAlertType, RoomWidgetUpdateRoomObjectEvent } from '../../../api';
+import { WidgetErrorBoundary } from '../../../common';
 import { useNitroEvent, useNotification, useRoom } from '../../../hooks';
 import { AvatarInfoWidgetView } from './avatar-info/AvatarInfoWidgetView';
 import { ChatInputView } from './chat-input/ChatInputView';
@@ -153,7 +154,7 @@ export const RoomWidgetsView: FC<{}> = props =>
         });
 
     return (
-        <>
+        <WidgetErrorBoundary name="RoomWidgets">
             <div className="absolute top-0 left-0 pointer-events-none size-full">
                 <FurnitureWidgetsView />
             </div>
@@ -169,6 +170,6 @@ export const RoomWidgetsView: FC<{}> = props =>
             <UserChooserWidgetView />
             <WordQuizWidgetView />
             <FriendRequestWidgetView />
-        </>
+        </WidgetErrorBoundary>
     );
 };

src/components/room/widgets/doorbell/DoorbellWidgetView.tsx

@@ -1,51 +1 @@
-import { FC, useEffect, useState } from 'react';
-import { LocalizeText } from '../../../../api';
-import { Button, Column, Grid, NitroCardContentView, NitroCardHeaderView, NitroCardView } from '../../../../common';
-import { useDoorbellWidget } from '../../../../hooks';
-
-export const DoorbellWidgetView: FC<{}> = props =>
-{
-    const [ isVisible, setIsVisible ] = useState(false);
-    const { users = [], answer = null } = useDoorbellWidget();
-
-    useEffect(() =>
-    {
-        setIsVisible(!!users.length);
-    }, [ users ]);
-
-    if(!isVisible) return null;
-
-    return (
-        <NitroCardView className="nitro-widget-doorbell" theme="primary-slim">
-            <NitroCardHeaderView headerText={ LocalizeText('navigator.doorbell.title') } onCloseClick={ event => setIsVisible(false) } />
-            <NitroCardContentView gap={ 0 } overflow="hidden">
-                <Column gap={ 2 }>
-                    <Grid className="text-black font-bold	 border-bottom px-1 pb-1" gap={ 1 }>
-                        <div className="col-span-6">{ LocalizeText('generic.username') }</div>
-                        <div className="col-span-6" />
-                    </Grid>
-                </Column>
-                <Column className="striped-children" gap={ 0 } overflow="auto">
-                    { users && (users.length > 0) && users.map(userName =>
-                    {
-                        return (
-                            <Grid key={ userName } alignItems="center" className="text-black border-bottom p-1" gap={ 1 }>
-                                <div className="col-span-6">{ userName }</div>
-                                <div className="col-span-6">
-                                    <div className="flex items-center gap-1 justify-end">
-                                        <Button variant="success" onClick={ () => answer(userName, true) }>
-                                            { LocalizeText('generic.accept') }
-                                        </Button>
-                                        <Button variant="danger" onClick={ () => answer(userName, false) }>
-                                            { LocalizeText('generic.deny') }
-                                        </Button>
-                                    </div>
-                                </div>
-                            </Grid>
-                        );
-                    }) }
-                </Column>
-            </NitroCardContentView>
-        </NitroCardView>
-    );
-};
+export { DoorbellWidgetView } from '../../../../features/doorbell';