refactor: rombak cache AI analisis image — pakai CDN URL langsung, hapus phash+sha

- Cache key image = CDN URL (query params stripped), bukan SHA data URL
  → re-analysis SAME attachment selalu cache-hit, berbeda attachment tidak kolisi
- Hapus perceptual hash (imghash dep + phash get/upsert/compute) sepenuhnya
- Hapus makeImageCacheKey hashing, ganti makeImageCacheKey yang return CDN URL
- textCacheStore, visionAnalyzer, mediaCache, mediaAnalysisClient updated
- imghash dependency removed from package.json
- Purge 82 stale cache rows (image: + phash:) dari DB

services/discord-gateway/src/modules/ai-moderation/mediaCache.ts

@@ -7,28 +7,22 @@
 import { LRUCache } from "lru-cache";
 import {
   acquireMediaAnalysisLock,
-  computeImagePhash,
   deleteCachedMediaAnalysis,
   getCachedMediaAnalysis,
-  getCachedMediaByPhash,
   makeCustomEmojiCacheKey,
   makeImageCacheKey,
   makeStickerCacheKey,
   upsertCachedMediaAnalysis,
-  upsertCachedMediaByPhash,
 } from "./textCacheStore.js";
 
 export {
   acquireMediaAnalysisLock,
-  computeImagePhash,
   deleteCachedMediaAnalysis,
   getCachedMediaAnalysis,
-  getCachedMediaByPhash,
   makeCustomEmojiCacheKey,
   makeImageCacheKey,
   makeStickerCacheKey,
   upsertCachedMediaAnalysis,
-  upsertCachedMediaByPhash,
 };
 
 /** Convenience alias for upsertCachedMediaAnalysis. */