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/App.css

@@ -0,0 +1,69 @@
+.app {
+  display: flex;
+  flex-direction: column;
+  height: 100vh;
+  background: #0c0c0c;
+}
+
+.titlebar {
+  flex: 0 0 auto;
+  display: flex;
+  align-items: center;
+  gap: 12px;
+  padding: 6px 12px;
+  background: #1a1a1a;
+  border-bottom: 1px solid #2a2a2a;
+  font-size: 12px;
+  color: #aaa;
+  user-select: none;
+}
+.titlebar .label {
+  font-weight: 600;
+  color: #ddd;
+}
+
+.distros, .presets {
+  display: flex;
+  gap: 4px;
+  align-items: center;
+}
+.distro-btn, .preset-btn, .palette-btn {
+  font: inherit;
+  font-family: "Cascadia Mono", "JetBrains Mono", "Consolas", monospace;
+  font-size: 11px;
+  background: #222;
+  color: #aaa;
+  border: 1px solid #333;
+  border-radius: 3px;
+  padding: 2px 8px;
+  cursor: pointer;
+}
+.distro-btn:hover, .preset-btn:hover, .palette-btn:hover {
+  background: #2a2a2a;
+  color: #ddd;
+}
+.distro-btn.active {
+  background: #1a3a5c;
+  color: #cce6ff;
+  border-color: #2a5a8c;
+}
+.preset-btn {
+  min-width: 28px;
+  text-align: center;
+}
+.muted {
+  color: #666;
+  font-style: italic;
+}
+.layout-info {
+  margin-left: auto;
+  font-family: "Cascadia Mono", "JetBrains Mono", "Consolas", monospace;
+  color: #777;
+  font-size: 11px;
+}
+
+.pane-wrap {
+  flex: 1 1 auto;
+  min-height: 0;
+  position: relative;
+}