Add history-ui workspace and supporting server endpoints

Splits history-ui out of asch/fix-everything into its own branch off
main. Includes the Svelte workspace, the three dedicated server
endpoints (list_vaults, fetch_vault_history, fetch_document_versions),
SPA asset embedding via rust-embed, and the matching TS mirror types in
sync-client.

Note: this branch will not compile against main on its own — the new
endpoints depend on database/error/config additions that live on
asch/fix-everything. Intended to be merged once asch/fix-everything
lands.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

frontend/history-ui/vite.config.ts

@@ -0,0 +1,15 @@
+import { defineConfig } from "vite";
+import { svelte } from "@sveltejs/vite-plugin-svelte";
+
+export default defineConfig({
+    plugins: [svelte()],
+    build: {
+        outDir: "dist",
+        emptyOutDir: true
+    },
+    server: {
+        proxy: {
+            "/vaults": "http://localhost:3010"
+        }
+    }
+});