docs: streamline trilingual Awesome JEV gallery

[erickkkyt]

What changed

• centers the title and project metrics across README variants
• adds an above-the-fold category index for all 10 use-case groups
• removes repeated explanatory sections and folds evidence notes into one compact disclosure
• adds a complete Japanese README alongside English and Simplified Chinese
• keeps the 10-project visual showcase and all 44 categorized project links in every language
• links each language to its matching BeatAPI gallery route

Verification

• npm test
• all 44 repositories appear in all three READMEs
• all featured evidence and original-case links match data/projects.json
• English, Chinese, and Japanese BeatAPI gallery routes return HTTP 200