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/Dockerfile

@@ -7,6 +7,7 @@ WORKDIR /build
 COPY package.json pnpm-workspace.yaml pnpm-lock.yaml tsconfig.base.json ./
 COPY apps/server/package.json ./apps/server/
 COPY apps/coder/package.json ./apps/coder/
+COPY apps/coder/web/package.json ./apps/coder/web/
 
 RUN pnpm install --frozen-lockfile
 
@@ -15,6 +16,7 @@ COPY apps/server ./apps/server
 RUN pnpm -C apps/server build
 
 COPY apps/coder ./apps/coder
+RUN pnpm -C apps/coder/web build
 RUN pnpm -C apps/coder build
 
 RUN pnpm deploy --filter=@boocode/coder --prod --legacy /out/coder
@@ -25,6 +27,7 @@ RUN apt-get update && apt-get install -y --no-install-recommends ripgrep git &&
 WORKDIR /app
 
 COPY --from=builder /out/coder ./
+COPY --from=builder /build/apps/coder/web/dist ./web
 
 ENV NODE_ENV=production
 EXPOSE 3000