style: migrate image assets to content-domain layout and align docs with new image rules

[RiskeyL]

Summary

This PR reorganizes the actual image files under the new rules and updates every docs page to match.

• Migrate 231 images from flat /images/ into a content-domain folder structure mirroring the top-level docs.json navigation. Each tutorial gets its own subfolder; workflow-101 splits per lesson.
• Normalize filenames (kebab-case, no retina suffix, lowercase extensions, zero-padded sequences) and rename 17 hash or CleanShot defaults to descriptive names.
• Delete 6 orphan images.
• Across en/, zh/, and ja/: update 705 references, wrap 850 bare markdown images in <Frame>, convert 202 raw <img> tags to markdown (no <img> tags remain), normalize alt text and captions to Title Case, translate 236 English alts in zh/ja, sync alt-to-caption in 176 Frames, and clear 106 awkward alts.

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Project	Status	Preview	Updated (UTC)
dify-core-product	🟢 Ready	View Preview	Apr 16, 2026, 11:27 AM

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