Add module slug autocomplete for `apply-set`

[renanfranca]

Summary

The Bash completion generated by:

seed4j completion bash --install

currently completes module slugs for seed4j apply because each visible module is registered as a Picocli subcommand.

In seed4j apply-set, module slugs are repeated positional arguments rather than subcommands. The current completion generator does not collect positional completion candidates, so this command does not suggest modules:

seed4j apply-set <TAB>

Expected behavior

The generated Bash completion should suggest visible module slugs for every module position:

seed4j apply-set <TAB>

Example suggestions:

init  maven-java  prettier  spring-boot

It should also filter suggestions by the current prefix:

seed4j apply-set init mav<TAB>

Expected suggestion:

maven-java

Modules already selected in the same command should not be suggested again because duplicate slugs are invalid. Hidden modules must never be suggested.

Generic apply-set options should remain available alongside module suggestions, and option value completion must continue working.

Implementation notes

• Expose the visible module slugs through the module-set planning boundary.
• Register those slugs as completion candidates for the repeated positional parameter.
• Extend BashCompletionScriptGenerator to collect positional candidates separately from subcommand candidates.
• Do not treat positional module slugs as command-path segments. After parsing apply-set init, the active command path must remain apply-set.
• Generate completion data statically, consistently with the existing apply completion. Users may regenerate the completion script when the runtime module catalog changes.

Acceptance criteria

• seed4j apply-set <TAB> suggests visible module slugs.
• Prefix filtering works for positional module slugs.
• Completion continues suggesting modules after one or more modules have already been entered.
• Already selected modules are not suggested again.
• Hidden modules are not suggested.
• Module slugs are not interpreted as subcommands by the completion script.
• apply-set options remain available during completion.
• Existing option value completion continues working.
• Existing completion behavior for seed4j apply <module> remains unchanged.
• The behavior is covered by generated-script integration tests, not only by assertions against script text.