fix: correct opencode release v1.4.3 linux-x64 tarball

fix: use opencode CLI binary instead of desktop deb (CONFIG_ERROR fix)

fix: add execute permission for start.sh to prevent runtime crash

fix: use start.sh as ENTRYPOINT to configure env

fix: use curl with retry for opencode download

fix: robust Dockerfile with retries

fix: normalize COPY instruction for stable builds

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