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/frontend/src/lib/api/messages.ts

@@ -1,5 +1,9 @@
 import { orpc } from "@/lib/orpc/client";
-import type { AttachmentRecord, MessageRecord } from "@/lib/types";
+import type {
+  AttachmentRecord,
+  MessageRecord,
+  SemanticSearchResult,
+} from "@/lib/types";
 
 export const messagesApi = {
   list: (
@@ -62,4 +66,11 @@ export const messagesApi = {
     orpc.analysis.search({ q, limit }) as unknown as Promise<{
       results: MessageRecord[];
     }>,
+
+  // Public semantic search over the persistent message archive (Qdrant).
+  semanticSearch: (query: string, limit?: number) =>
+    orpc.messages.semanticSearch({ query, limit }) as unknown as Promise<{
+      results: SemanticSearchResult[];
+      nextCursor: null;
+    }>,
 };

services/frontend/src/lib/types/message.ts

@@ -163,3 +163,17 @@ export interface AttachmentRecord {
   created_at: number;
   uploaded_at?: number | null;
 }
+
+// ── Semantic Search (read-only public archive search) ──────────
+
+export interface SemanticSearchResult {
+  message_id: string | null;
+  content: string;
+  score: number;
+  created_at: number;
+}
+
+export interface SemanticSearchResponse {
+  results: SemanticSearchResult[];
+  nextCursor: null;
+}

services/frontend/src/lib/types/moderation.ts

@@ -21,6 +21,14 @@ export interface ModerationAction {
   executed_at: number | null;
   username: string | null;
   content: string | null;
+  // ── Explainability (structured verdict, surfaced read-only to public web) ──
+  flags: string[] | null;
+  categories: string[] | null;
+  severity: "none" | "low" | "medium" | "high" | "critical" | null;
+  confidence: number | null;
+  score: number | null;
+  evidence: string[] | null;
+  policy_version: string | null;
 }
 
 export interface ModerationStats {