Address code-split review: chunk-load recovery + tidier lazy + gesture split

Gadfly on #106:

- (2 models) React.lazy memoizes a REJECTED import, so after a deploy (every
  main push) a still-open app references chunk hashes the server just
  replaced — the import 404s and RouteError's "Try again" can never recover.
  New lazyPage() helper reloads once on a chunk-load failure to fetch fresh
  hashes (session-flag guarded against a reload loop; cleared on success).
- (perf) @use-gesture is editor-only, but the single vendor chunk pulled it
  into the eager first paint. Exclude it from vendor so it rides with the
  lazy editor chunk (vendor 421→392 KB; the gesture code moved into the
  editor's own chunk). react/react-dom/tanstack still share one vendor chunk
  — splitting react-dom out is what broke React 19 at load.
- (nits) lazyPage also unwraps the named export, so the five route lazies are
  uniform one-liners; moved the lazy block below the import group.

Re-verified live: app mounts, /gardens/1 lazy-loads + renders the editor,
console clean. tsc + build green, no >500 KB warning.

Co-Authored-By: Claude Opus 4.8 (1M context) <[email protected]>
Claude-Session: https://claude.ai/code/session_01H3zbym8Doka2d7D48maSgZ

web/vite.config.ts

@@ -39,7 +39,14 @@ export default defineConfig(({ mode }) => {
           // routes are code-split separately via React.lazy (router.tsx), which is
           // where the real first-paint win is.
           manualChunks(id) {
-            return id.includes('node_modules') ? 'vendor' : undefined
+            if (!id.includes('node_modules')) return undefined
+            // Editor-only libs (the gesture engine) ride with the lazy editor
+            // chunk instead of the eager vendor one, so the first paint doesn't
+            // pay for code only the canvas needs. Everything else — react, tanstack
+            // and the rest — stays in ONE vendor chunk; splitting react-dom out
+            // reorders its init across chunks and breaks React 19 at load.
+            if (id.includes('@use-gesture')) return undefined
+            return 'vendor'
           },
         },
       },