Add Google Search Console CLI commands and auth scopes

[aesadde]

Summary

• add a new searchconsole top-level command group (aliases: gsc, webmasters)
• implement Search Console operations:
  • sites list|get
  • searchanalytics query (plus searchconsole query shortcut)
  • sitemaps list|get|submit|delete
• add a dedicated webmasters API client wrapper in internal/googleapi
• extend auth service model with searchconsole and readonly/full scope resolution
• update README with Search Console setup and quick-test examples

Why

This adds an agent-friendly, scriptable way to pull Google Search Console data from CLI while preserving gogcli's existing auth and least-privilege scope model.

Validation

• go test ./... passes
• gog searchconsole --help shows new command group
• gog auth services --json includes searchconsole service/scopes

[salmonumbrella]

Fantastic! Thank you @aesadde!

cc: @visionik