feat(archive): rich metadata in semantic search — username/channel/guild context + guild filter

Archive payload now stores username, channel_id, guild_id, thread_id and the
real message created_at (not embed time). Backend searchArray accepts an
optional guildId and applies a Qdrant payload filter so results can be scoped
to the guild being viewed. API/frontend expose the new fields and the
semantic results card shows who said it, in which channel, and when —
turning bare text blobs into contextual results. Old points fall back to
analyzed_at and omit the new fields gracefully.

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

@@ -70,8 +70,12 @@ export const messagesApi = {
     }>,
 
   // Public semantic search over the persistent message archive (Qdrant).
-  semanticSearch: (query: string, limit?: number) =>
-    orpc.messages.semanticSearch({ query, limit }) as unknown as Promise<{
+  semanticSearch: (query: string, limit?: number, guildId?: string) =>
+    orpc.messages.semanticSearch({
+      query,
+      limit,
+      ...(guildId ? { guildId } : {}),
+    }) as unknown as Promise<{
       results: SemanticSearchResult[];
       nextCursor: null;
     }>,