ci: prewarm the JetBrains image Bun package cache

Co-authored-by: kiloconnect[bot] <240665456+kiloconnect[bot]@users.noreply.github.com>

packages/containers/README.md

@@ -8,7 +8,7 @@ Images
 
 - `base`: Ubuntu 24.04 with common build tools and utilities
 - `bun-node`: `base` plus Bun and Node.js 24
-- `jetbrains`: `bun-node` plus Java 21 and the pre-cached Gradle distribution
+- `jetbrains`: `bun-node` plus Java 21, JBR font libraries, and pre-cached Gradle and Bun packages <!-- kilocode_change -->
 - `rust`: `bun-node` plus Rust (stable, minimal profile)
 - `tauri-linux`: `rust` plus Tauri Linux build dependencies
 - `publish`: `bun-node` plus Docker CLI and AUR tooling

packages/containers/jetbrains/Dockerfile

@@ -1,7 +1,18 @@
 # kilocode_change start
 ARG REGISTRY=ghcr.io/kilo-org
+FROM ${REGISTRY}/build/bun-node:24.04 AS bun-cache
+
+WORKDIR /src
+COPY package.json bun.lock bunfig.toml ./
+COPY packages ./packages
+COPY patches ./patches
+RUN bun install --frozen-lockfile --ignore-scripts --cache-dir=/bun-cache
+
 FROM ${REGISTRY}/build/bun-node:24.04
 
+COPY --from=bun-cache /bun-cache/ /opt/bun/install/cache/
+ENV BUN_INSTALL_CACHE_DIR=/opt/bun/install/cache
+
 ARG DEBIAN_FRONTEND=noninteractive
 ARG GRADLE_VERSION=9.4.1