feat: add --update-bundle with provenance-aware conflict handling

Updates re-clone a bundle's recorded source (honoring a recorded commit
pin unless a #<ref> override moves it), silently refresh files the bundle
owns that the user never modified, and fall back to the normal conflict
prompts for modified or unowned files. Files the remote no longer ships
are offered for deletion (kept by default non-interactively, staying
owned). The record is refreshed with the new commit, version, and
metadata, and stamped with an updated_at timestamp on success.

src/config/mod.rs

@@ -32,7 +32,7 @@ pub use self::app_config::AppConfig;
 pub use self::app_state::AppState;
 pub use self::bundles::list_installed_bundles;
 pub use self::input::Input;
-pub use self::install_remote::{install_remote, install_remote_from_repl_args};
+pub use self::install_remote::{install_remote, install_remote_from_repl_args, update_bundle};
 pub use self::macro_policy::{
     MacroAllowlistLevel, MacroPolicy, MacroSource, MacroState, RESERVED_MACRO_NAMES, ResolvedMacro,
 };