Remove v1.4 doc from Docusaurus build

[jillian-maroket]

Issue

The Docusaurus build fails with the following error message:

[Rspack Deprecation] `experiments.lazyBarrel` config is deprecated and will be removed in Rspack v2.0. Lazy barrel is already stable and enabled by default. Remove this option from your Rspack configuration.
Error: The operation was canceled.

I first encountered this issue in PR #1134 (created on 2026/9/16). The error message disappeared after I merged main into my branch.

Root cause

@votdev offered the following analysis in Slack:

The build failure in GitHub Actions is caused by an Out-Of-Memory (OOM Killer) condition (exit code 137 / SIGKILL), which the runner reports as The operation was canceled.

• GitHub-hosted ubuntu-latest runners have a strict memory ceiling of 7 GB RAM.
• With v1.9 added alongside v1.4, Docusaurus is trying to compile 7 doc versions simultaneously (current/dev + v1.9 through v1.4). Rspack (native memory) together with Node.js V8 heap exceeds the runner's available memory.

Mitigation

@votdev suggested retiring v1.4 from the active build (the files stay preserved under versioned_docs/, but are omitted from the build config). I initially pushed back because of the following reasons:

• We typically include the latest EOL doc in the build.
• The EOL date for v1.5.x (according to the Support Matrix is 30 December 2026, so I cannot apply the EOL label yet.

However, the error occurred again today, so I have decided to remove v1.4 (with @Vicente-Cheng's consent).

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[votdev]

I switched to draft to prevent merging before tests on #1139 are finished. Using more swap might prevent us from removing the 1.4 version atm.

[votdev]

I would suggest to keep that PR open for a while if it comes out that the increased swap memory does not fully fix the issue. If we do not realize problems for some time, we can safely close this PR.