Document public APIs with YARD

[mackuba]

Motivation

• Expand documentation coverage to include public methods on core DIDKit types and helpers to improve generated YARD docs and developer discoverability.
• Clarify HTTP and resolver behavior by annotating request helpers and resolver options/returns so callers understand expected inputs and error conditions.
• Surface error accessors and service/handle parsing behavior to make troubleshooting and integration simpler.

Description

• Added YARD-style comments for public methods across AtHandles (parse_also_known_as), Services (get_service, pds_endpoint, labeler_endpoint, pds_host, labeler_host) and ServiceRecord initializer with error notes.
• Documented HTTP helpers in Requests (get_response, get_data, get_json, content_type_matches, uri_origin) and enhanced APIError in errors.rb with accessor docs for status and body.
• Annotated resolver and DID behaviors in Resolver (initialization options, DNS/well-known resolution, DID/document resolution, verified-handle helpers) and in DID/Document (constructors, get_document, get_verified_handle, account_status, web_domain) with param/return/error details.
• Added short namespace comments in lib/didkit.rb and lib/didkit/version.rb and updated several files with inline docs only; no functional logic changes were introduced.

Testing

• No automated tests were executed for this change.

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Codex Task