feat(gmw): moderation explainability + semantic message search

- Persist structured verdict (flags/severity/confidence/evidence) on
  moderation_actions so the public web can show WHY a message was moderated.
- Add a persistent Qdrant archive collection (gmw_message_archive); embed
  every captured message at capture time (fire-and-forget, best-effort).
- Public semantic search over the archive (backend oRPC + FE toggle on the
  messages view). Both features are read-only/public and fully automatic.

Migration: 0015_add_moderation_explainability.sql

services/backend/src/shared/config/index.ts

@@ -134,6 +134,7 @@ export const configSchema = z
       .default("https://9router.asepharyana.my.id/v1"),
     AI_LLM_MODEL: z.string().default("text"),
     AI_LLM_VISION_MODEL: z.string().optional(),
+    AI_LLM_EMBEDDING_MODEL: z.string().optional(),
     AI_LLM_MAX_CONCURRENT: z.coerce.number().int().positive().default(5),
     AI_LLM_IMAGE_MAX_DIMENSION: z.coerce
       .number()
@@ -208,6 +209,11 @@ export const configSchema = z
       .default("https://api.openai.com/v1"),
     OPENAI_MODERATION_MODEL: z.string().default("omni-moderation-latest"),
 
+    // ── Qdrant (message archive for semantic search) ──────────────────
+    QDRANT_URL: z.string().optional(),
+    QDRANT_API_KEY: z.string().optional(),
+    QDRANT_ARCHIVE_COLLECTION: z.string().default("gmw_message_archive"),
+
     // ── Auto Delete ─────────────────────────────────────────────────────
     AUTO_DELETE_FLAGGED_ENABLED: z
       .string()