fix(deps): update PATH immediately after rustup install

After the rustup installer runs, add the cargo bin dir to PATH in the
current session so subsequent installs in the same fish-deps run can
find cargo without a shell restart. Checks CARGO_HOME/bin first (set
in config.fish), then falls back to the rustup default ~/.cargo/bin.
Warns the user if cargo still isn't detectable after the path update.

functions/_fish_deps_install.fish

@@ -101,7 +101,7 @@ function _fish_deps_install
                     set m (math $m + 1)
                 end
                 read -l -P "  Choose [1-"(count $methods)"] (default 1 = $method_labels[1]): " _choice
-                if test -n "$_choice"; and test "$_choice" -ge 1; and test "$_choice" -le (count $methods)
+                if string match -qr '^\d+$' "$_choice"; and test "$_choice" -ge 1; and test "$_choice" -le (count $methods)
                     set chosen_method $methods[$_choice]
                 end
             else
@@ -116,6 +116,19 @@ function _fish_deps_install
                     _fish_deps_pm_install $pm_pkg
                 case special-rustup
                     curl https://sh.rustup.rs -sSf | sh
+                    # Add cargo to PATH for the rest of this session without restarting.
+                    # Try CARGO_HOME first (set in config.fish), then the rustup default.
+                    for _d in "$CARGO_HOME/bin" "$HOME/.cargo/bin"
+                        if test -d "$_d"
+                            fish_add_path "$_d"
+                            break
+                        end
+                    end
+                    if not type -q cargo
+                        set_color yellow
+                        echo "  cargo not yet in PATH — restart your shell if subsequent installs fail."
+                        set_color normal
+                    end
                 case special-fzf
                     fzf-update
                 case special-fisher