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/package.json

@@ -6,7 +6,8 @@
         "obsidian-plugin",
         "test-client",
         "deterministic-tests",
-        "local-client-cli"
+        "local-client-cli",
+        "history-ui"
     ],
     "prettier": {
         "trailingComma": "none",