feat(completion): complete enum flag values from schema

[levontumanyan]

Summary

Extends tab completion to offer valid enum values when typing a flag value — e.g. elastic stack es cat nodes --h <TAB> now shows all available cat node column names.

Approach

• extractSchemaArgs() in schema-args.ts now calls a new extractEnumValues() helper that walks z.enum, union(z.enum, z.string), optional, and lazy wrappers to pull out enum values. These are stored as enumValues?: readonly string[] on SchemaArgDefinition.
• defineCommand() in factory.ts attaches a non-enumerable _enumCompleters: Map<string, () => string[]> to each Commander command object for every enum-typed flag.
• enumerate() checks _enumCompleters on the current command as a fallback when the global registry has no completer for the previous flag. Both --flag <TAB> and --flag=partial<TAB> forms are handled.

Since enum values come directly from the generated Zod schemas (e.g. CatCatNodeColumn), all cat API column flags and any other enum-typed flags across the codebase get completions automatically with no manual registration needed.

Test plan

• extractSchemaArgs -- enumValues suite (5 new tests): plain enum, optional wrapper, union(enum, string) pattern, non-enum fields
• enumerate -- command-level enum completers suite (4 new tests): basic invocation, prefix-filter, --flag=partial form, registry priority
• npm test — 1472/1472 pass
• Manual: elastic stack es cat nodes --h <TAB> lists all cat node column names

🤖 Generated with Claude Code

[levontumanyan]

Closing — not needed. The flag value completion is out of scope for now; the original ask was positional (context name) completion only (PR #424).