优化 Dockerfile，统一基础镜像定义

Co-authored-by: Copilot <copilot@github.com>

Dockerfile

@@ -1,13 +1,14 @@
-# syntax=docker/dockerfile:1.7
+FROM oven/bun:canary-slim AS base
+
+FROM base AS deps
 
-FROM oven/bun:canary-slim AS deps
 WORKDIR /app
 
 COPY package.json bun.lock ./
 COPY .opencode/package.json .opencode/bun.lock ./.opencode/
 RUN bun install --frozen-lockfile
 
-FROM deps AS build
+FROM base AS build
 WORKDIR /app
 
 COPY tsconfig.json opencode.json README.md ./
@@ -15,7 +16,7 @@ COPY src ./src
 COPY .opencode ./.opencode
 RUN bun run check
 
-FROM oven/bun:canary-slim AS runner
+FROM base AS runner
 WORKDIR /app
 
 ENV NODE_ENV=production