feat: rename install flags and unify .install dispatch

--install now takes a git URL or an installed bundle name: categories
are redirected to the new --install-builtins, installed names become
implicit updates, and source-shaped values install remotely. The old
--install-from keeps its exact behavior as a hidden deprecated alias.
The REPL's .install gains the same unified dispatch while keeping
.install <category> and .install remote <url> back-compat.

src/main.rs

@@ -130,11 +130,18 @@ async fn main() -> Result<()> {
 
     install_builtins()?;
 
-    if let Some(category) = cli.install {
+    if let Some(category) = cli.install_builtins {
         return config::install_assets(category);
     }
 
+    if let Some(value) = cli.install.as_deref() {
+        return config::install_or_update(value, cli.filter, cli.install_force);
+    }
+
     if let Some(url) = cli.install_from.as_deref() {
+        eprintln!(
+            "warning: --install-from is deprecated and will be removed in a future release; use --install <GIT_URL>"
+        );
         return config::install_remote(url, cli.filter, cli.install_force);
     }