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/package.json

@@ -28,7 +28,6 @@
     "discord.js-selfbot-v13": "^3.7.1",
     "dotenv": "^17.4.2",
     "drizzle-orm": "^0.45.2",
-    "imghash": "^1.1.4",
     "ioredis": "^5.11.0",
     "libsodium-wrappers": "^0.8.4",
     "lru-cache": "^11.5.1",