Migrate frontend from Svelte 5 to React 18

After hours of fighting Svelte 5's prop-reactivity through the
recursive Pane → SplitNode → LeafPane chain (props captured at
mount, never updated; context+getter pattern crashed; DOM-direct
workarounds created zombie-split click-intercept bugs), we
checkpointed the Svelte version (branch svelte-archive at e9015b2,
tarball at D:\archives\tiletopia-svelte-2026-05-22.tar.gz) and
rewrote the frontend in React.

Kept verbatim:
- All of src-tauri/ (Rust backend, Tauri config, icons)
- scripts/ (make-icon.py, release.sh)
- README.md, CLAUDE.md, memory.md
- src/lib/layout/tree.ts (pure TS — 43 tests still pass)
- src/ipc.ts (Tauri command wrappers)

Rewrote in React:
- src/App.tsx (top-level state via useState, OrchestrationProvider
  for descendants via React.Context)
- src/lib/layout/orchestration.tsx (React Context API for shared
  state — known-reliable reactivity, no Svelte 5 wall)
- src/lib/layout/Pane.tsx (recursive dispatcher)
- src/lib/layout/SplitNode.tsx (draggable gutter, local ratio state)
- src/lib/layout/LeafPane.tsx (toolbar + XtermPane)
- src/components/XtermPane.tsx (xterm.js wrapper, refs for callbacks)
- src/components/Notifications.tsx, Palette.tsx

Build: Vite + @vitejs/plugin-react. TypeScript strict. Same Tauri 2
config. Verified: pnpm check (clean), pnpm test (43/43 pass).
Not yet verified: pnpm tauri dev — that requires the Windows host.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/lib/layout/orchestration.tsx

@@ -0,0 +1,58 @@
+import { createContext, useContext, type ReactNode } from "react";
+import type { Orientation, NodeId } from "./tree";
+import type { PaneId } from "../../ipc";
+
+/**
+ * Orchestration context — every piece of shared state and every operation
+ * that a Pane / SplitNode / LeafPane might call. Lives in React context so
+ * descendants can `useOrchestration()` without prop drilling.
+ *
+ * activeLeafId comes in as a plain value (re-derived by App's useState).
+ * React's context is reactive: when the App-level Provider updates the
+ * value, ALL consumers re-render. No Svelte-style props-don't-propagate
+ * trap here.
+ */
+export interface Orchestration {
+  // Read-only state
+  activeLeafId: NodeId | null;
+  distros: string[];
+
+  // Tree mutations
+  split: (leafId: NodeId, orientation: Orientation) => void;
+  close: (leafId: NodeId) => void;
+  setDistro: (leafId: NodeId, distro: string) => void;
+  setLabel: (leafId: NodeId, label: string | undefined) => void;
+  toggleBroadcast: (leafId: NodeId) => void;
+
+  // Per-pane orchestration
+  setActive: (leafId: NodeId) => void;
+  registerPaneId: (leafId: NodeId, paneId: PaneId | null) => void;
+  broadcastFrom: (originLeafId: NodeId, dataB64: string) => void;
+  notify: (message: string) => void;
+}
+
+const OrchestrationContext = createContext<Orchestration | null>(null);
+
+export function OrchestrationProvider({
+  value,
+  children,
+}: {
+  value: Orchestration;
+  children: ReactNode;
+}) {
+  return (
+    <OrchestrationContext.Provider value={value}>
+      {children}
+    </OrchestrationContext.Provider>
+  );
+}
+
+export function useOrchestration(): Orchestration {
+  const orch = useContext(OrchestrationContext);
+  if (!orch) {
+    throw new Error(
+      "useOrchestration() must be called inside <OrchestrationProvider>",
+    );
+  }
+  return orch;
+}