Preserve intentional email indentation

[parterburn]

Summary

• distinguish Gmail-authored indentation from actual .gmail_quote reply history
• recover sanitized <blockquote> markup only when it exactly matches Griddler’s already-isolated plain reply
• remove Gmail history and signature containers before validating recovered indentation
• preserve indented text for free users as plain formatting
• reject attributed quotes, mismatched text, and active raw HTML
• retain the complete uniformly spaced fallback from the prior Mailgun fix

Verification

• bundle exec rspec spec/models/email_processor_spec.rb spec/features/entries_spec.rb — 54 examples, 0 failures
• bundle exec rspec — 252 examples, 0 failures, 1 expected pending
• CI vm-job and CodeFactor pass
• manually processed a reply containing authored indentation plus actual outbound history; indentation renders and history/signature remain absent