v2.0.0: BooCoder frontend — chat pane + diff pane + session picker

Phase 3 of v2.0. React + Vite SPA at apps/coder/web/ served by
the coder Fastify server via @fastify/static with SPA fallback.

Chat pane: message list via WS streaming (useSessionStream hook),
input bar, POST /api/sessions/:id/messages on submit, markdown
rendering via react-markdown + remark-gfm, inline tool-call display.

Diff pane: fetches GET /api/sessions/:id/pending, shows pending
changes with file path + operation badge (create/edit/delete),
before/after diff for edits, Approve/Reject per change and
Approve All/Reject All buttons.

Layout: fixed two-pane split (chat 60%, diff 40%). Dark theme
(bg-zinc-900). Desktop-first for v2.0.0.

Session picker (Home page): lists projects and sessions from the
shared DB. No CRUD — use BooChat's UI for that.

Dockerfile updated: builds web app in builder stage, copies dist
to runtime. index.ts registers fastifyStatic + SPA fallback route.

Tailwind v4, React 18, TypeScript strict. ~20 new files, ~370KB
built output. Functional developer tool UI, not polished consumer
product — Phase 7 (v2.0.3) handles polish.

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

apps/coder/web/src/globals.css

@@ -0,0 +1,22 @@
+@import "tailwindcss";
+
+body {
+  margin: 0;
+  min-height: 100vh;
+}
+
+/* Scrollbar styling for dark theme */
+::-webkit-scrollbar {
+  width: 8px;
+  height: 8px;
+}
+::-webkit-scrollbar-track {
+  background: transparent;
+}
+::-webkit-scrollbar-thumb {
+  background: #3f3f46;
+  border-radius: 4px;
+}
+::-webkit-scrollbar-thumb:hover {
+  background: #52525b;
+}