Import entries as block content

[cbravobernal]

Summary

• Serialize imported headings, paragraphs, and lists as Gutenberg block markup.
• Append imported media as an Image block for one image or a Gallery block with nested Image blocks for multiple images.
• Bump import schema to reprocess older completed imports on rerun.
• Expand pure/wp-env fixture assertions for parseable blocks and image classes.

Radical Pipelines

• spec-writer + spec-reviewer approved
• plan-writer + plan-reviewer requested changes
• plan-writer-2 + plan-reviewer-2 approved
• implementer completed changes
• code-reviewer approved

Verification

• PHP lint excluding private/local paths
• php tests/pure-helper-tests.php
• WP_ENV_PORT=8898 wp-env ... tests/wp-env-import-sample.php passed
• git diff --check

Fixes #10