feat(skins): add skin color extraction and filtering (Issue #15)

[KitDoesIt]

Done - see KitDoesIt/teeworlds.cn PR

[kilo-code-bot]

Code Review Summary

Status: No Issues Found | Recommendation: Merge

Files Reviewed (6 files)

• src/lib/server/db/skins.ts - Database schema update for RGB colors
• src/lib/server/fetches/skins.ts - Cache version bump (6 → 7)
• src/lib/server/skin-cache.ts - Dominant color extraction for non-grayscale skins
• src/routes/api/skin-colors/+server.ts - New API endpoint for skin colors
• src/routes/ddnet/skins/+page.svelte - Color filter UI
• src/routes/ddnet/skins/+page.ts - Load skin colors data

Observations

• Database migration uses CREATE TABLE IF NOT EXISTS which is safe for existing deployments
• Cache version incremented correctly to invalidate old entries without color data
• Color extraction uses proper quantization (16-level) and ignores transparent pixels
• Filter logic correctly handles edge cases (null hue, missing color data)

---

_{Reviewed by minimax-m2.5-20260211 · 260,560 tokens}

[KitDoesIt]

@TsFreddie 这是一个 PR review 请求，来自 KitDoesIt 的皮肤颜色提取和过滤功能 (Issue #15)。需要我执行 review 吗？