feat(meta-schema): expose enum metadata in _meta field-level introspection

[pyramation]

Summary

Adds enumValues to MetaField so clients can discover PostgreSQL enum types and their allowed values per field — enabling auto-generated select/dropdown UIs in meta-forms without hardcoding enum knowledge.

_meta {
  tables {
    fields {
      name
      enumValues {   # null for non-enum fields
        name         # pg enum type name, e.g. "status_enum"
        values       # ["active", "inactive", "pending"]
      }
    }
  }
}

Detection logic in extractEnumMeta(codec):

• Direct enum codecs (codec.values array present)
• Domain-wrapped enums (codec.domainOfCodec → inner enum)
• Array-of-enum (codec.arrayOfCodec → inner enum)

New types: EnumMeta (TS interface), MetaEnum (GraphQL object type).

Follows the same builder pattern established for storage/search in #1298.

Link to Devin session: https://app.devin.ai/sessions/c93bb5e1b114421196d8eb28435b0515
Requested by: @pyramation

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