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>

sync-server/src/app_state/database/models.rs

@@ -83,24 +83,6 @@ pub struct DocumentVersion {
     pub device_id: DeviceId,
 }
 
-/// Row struct for vault history queries (used by `sqlx::query_as!`)
-#[derive(Debug)]
-pub struct VaultHistoryRow {
-    pub vault_update_id: VaultUpdateId,
-    pub creation_vault_update_id: VaultUpdateId,
-    pub document_id: DocumentId,
-    pub relative_path: String,
-    pub updated_date: DateTime<Utc>,
-    pub is_deleted: bool,
-    pub user_id: String,
-    pub device_id: String,
-    pub content_size: Option<u64>,
-}
-
-pub struct VaultStats {
-    pub created_at: Option<DateTime<Utc>>,
-    pub document_count: u32,
-}
 
 impl From<StoredDocumentVersion> for DocumentVersion {
     fn from(value: StoredDocumentVersion) -> Self {