fix: pin Dockerfile bun version to match lockfile

oven/bun:1 resolved to 1.3.10 which considers the lockfile stale.
Pin to 1.3.6 to match the version that generated bun.lock.

Author: richiemcilroy

apps/api/Dockerfile

@@ -1,4 +1,4 @@
-FROM oven/bun:1 AS deps
+FROM oven/bun:1.3.6 AS deps
 WORKDIR /app
 
 COPY package.json bun.lock ./
@@ -18,7 +18,7 @@ COPY . .
 RUN bun run --filter @sandchest/contract build && \
     bun run --filter @sandchest/api build
 
-FROM oven/bun:1-slim
+FROM oven/bun:1.3.6-slim
 WORKDIR /app
 
 ENV NODE_ENV=production