docs: update architecture and plan for tree inspector UI

Record the viewer-registry decision and refresh the extract/web
descriptions and repo layout.

docs/implementation-plan.md

@@ -78,7 +78,9 @@ tts-workshop/
 │           │   ├── SearchPage.tsx
 │           │   └── ModPage.tsx
 │           ├── components/
-│           │   └── SearchResults.tsx
+│           │   ├── SearchResults.tsx
+│           │   ├── ObjectTree.tsx     # containment-tree sidebar
+│           │   └── viewers.tsx        # viewer registry + default viewer
 │           └── stores/
 │               ├── searchStore.ts  # zustand
 │               └── modStore.ts     # zustand
@@ -145,6 +147,9 @@ Isomorphic analysis of a parsed `TTSMod`. No Node-specific APIs.
   - `flattenObjects(mod)` — all objects in the tree.
   - `filterObjects(mod, predicate)` — filter by name, GUID, type, etc.
   - `findObject(mod, guid)` — lookup by GUID.
+  - `buildTree(mod)` — containment tree (`{ object, label, children }`),
+    mirroring how TTS nests objects; `label` is `Nickname` when present,
+    else the class `Name`.
   - `traverseMod` / `markParent` (moved from `tts`).
   - Returns lightweight graph shapes: `{ guid, name, type, parentGuid,
     childrenGuids, refs }`.
@@ -195,9 +200,14 @@ proxy API and `packages/extract` directly for analysis.
   `modFileUrl` helper for the raw-file download.
 - `pages/SearchPage.tsx` — search form, drives `searchStore`.
 - `pages/ModPage.tsx` — loads the mod via `modStore`, uses `@tts/extract`
-  (`flattenObjects`, `collectRefs`) to render objects and asset refs, and links
-  to the raw save file.
+  (`buildTree`, `collectRefs`) to render a containment-tree sidebar and an
+  inspector pane for the selected object, and links to the raw save file.
 - `components/SearchResults.tsx` — result grid + pagination.
+- `components/ObjectTree.tsx` — recursive tree sidebar; each entry shows a
+  class tag + display label, indented by depth. Clicking selects an object.
+- `components/viewers.tsx` — viewer registry (`registerViewer` /
+  `resolveViewer`) plus a `DefaultViewer` that renders an object's fields;
+  custom per-class viewers can be registered later.
 - `stores/searchStore.ts` / `stores/modStore.ts` — Zustand stores for search
   and mod state.
 - `vite.config.ts` — dev proxy for `/search`, `/items`, `/health` →