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>

sync-server/Cargo.toml

@@ -34,6 +34,8 @@ bimap = "0.6.3"
 ts-rs =  { version = "10.1", features = ["uuid-impl", "chrono-impl"] }
 base64 = "0.22.1"
 reconcile-text = { version = "0.8.0", features = ["serde"] }
+rust-embed = "8.5"
+mime_guess = "2.0"
 
 [profile.release]
 codegen-units = 1