fix(custom generators): prioritize custom generator JAR when provided

[smolnikov]

• Skip Maven JAR download when --custom-generator is provided, allowing the CLI to run with only a custom JAR
• When the standard JAR is already present, both JARs are still combined on the classpath (preserving existing behavior for custom generators that extend base classes)
• Detect --custom-generator from process.argv early in bootstrap, before Commander parses, so the flag is available during init() command discovery

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Summary by cubic

Prioritize a user-provided custom generator JAR. If --custom-generator is passed, the CLI skips downloading the standard JAR and uses only the custom JAR when the standard one is missing; otherwise both are added to the classpath.

• Bug Fixes
  • Skip version lookup and download when --custom-generator is present.
  • Use only the custom JAR if the standard JAR is absent; otherwise combine both on the classpath.
  • Detect --custom-generator early from process.argv (supports --custom-generator <path> and --custom-generator=<path>).

^{Written for commit 70ceec1. Summary will update on new commits.}

[cubic-dev-ai]

No issues found across 6 files

[wing328]

looks good to me

thanks for the enhancement

[github-actions]

🎉 This PR is included in version 2.31.1 🎉

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

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