Remove history-ui workspace and supporting server endpoints

Splits history-ui out of asch/fix-everything into its own branch. This
commit removes from asch/fix-everything: the Svelte workspace under
frontend/history-ui, the three dedicated server endpoints (list_vaults,
fetch_vault_history, fetch_document_versions) and their router wiring,
the SPA asset embedding in index.rs, the rust-embed/mime_guess deps,
the build.rs dist-dir creation, the matching response types and
database methods (list_vaults, get_vault_stats, get_vault_history,
get_document_versions, VaultStats, VaultHistoryRow), and the TS mirror
types in sync-client.

Note: Cargo.lock, frontend/package-lock.json, and sync-server/.sqlx/
will need regeneration via `cargo build`, `npm install`, and
`cargo sqlx prepare` to clean up stale entries. The history-ui mentions
in CLAUDE.md and scripts/update-api-types.sh predate this branch (also
present on main) and were left as-is.

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

frontend/package.json

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