feat: add Zero queries for all 6 synced tables

Define named queries matching each Electric hook's data needs:
- notifications.byUser (use-inbox)
- documents.bySpace (use-documents, use-documents-processing)
- connectors.bySpace (use-connectors-electric)
- messages.byThread (use-messages-electric)
- comments.byThread (use-comments-electric)
- chatSession.byThread (use-chat-session-state)

Also moves schema files from zero/tables/ to zero/schema/ for
consistent modular folder structure.

surfsense_web/zero/schema/inbox.ts

@@ -0,0 +1,16 @@
+import { table, string, number, boolean, json } from "@rocicorp/zero";
+
+export const notificationTable = table("notifications")
+	.columns({
+		id: number(),
+		userId: string().from("user_id"),
+		searchSpaceId: number().optional().from("search_space_id"),
+		type: string(),
+		title: string(),
+		message: string(),
+		read: boolean(),
+		metadata: json().optional(),
+		createdAt: number().from("created_at"),
+		updatedAt: number().optional().from("updated_at"),
+	})
+	.primaryKey("id");